This repo contains solutions for projecteuler problems. Specially created for newcomers to contribute as part of Hacktoberfest Challenge.
- Problem #1 Multiples of 3 and 5 || solutions
- Problem #2 Even Fibonacci numbers || solutions
- Problem #3 Largest prime factor || solutions
- Problem #4 Largest palindrome product || solutions
- Problem #5 Smallest multiple || solutions
- Problem #6 Sum square difference || solutions
- Problem #7 10001st prime || solutions
- Problem #8 Largest product in a series || solutions
- Problem #9 Special Pythagorean triplet || solutions
- Problem #10 Summation of primes || solutions
- Problem #11 Largest product in a grid || solutions
- Problem #12 Highly divisible triangular number || solutions
- Problem #13 Large sum || solutions
- Problem #14 Longest Collatz sequence || solutions
- Problem #15 Lattice paths || solutions
- Problem #16 Power digit sum || solutions
- Problem #17 Number letter counts || solutions
- Problem #18 Maximum path sum I || solutions
- Problem #19 Counting Sundays || solutions
- Problem #20 Factorial digit sum || solutions
- Problem #21 Amicable numbers || solutions
- Problem #22 Names scores || solutions
- Problem #23 Non-abundant sums || solutions
- Problem #24 Lexicographic permutations || solutions
- Problem #25 1000-digit Fibonacci number || solutions
- Problem #26 Reciprocal cycles || solutions
- Problem #27 Quadratic primes || solutions
- Problem #28 Number spiral diagonals || solutions
- Problem #29 Distinct powers || solutions
- Problem #30 Digit fifth powers || solutions
- Problem #31 Coin sums || solutions
- Problem #32 Pandigital products || solutions
- Problem #33 Digit cancelling fractions || solutions
- Problem #34 Digit factorials || solutions
- Problem #35 Circular primes || solutions
- Problem #36 Double-base palindromes || solutions
- Problem #37 Truncatable primes || solutions
- Problem #38 Pandigital multiples || solutions
- Problem #39 Integer right triangles || solutions
- Problem #40 Champernowne's constant || solutions
- Problem #41 Pandigital prime || solutions
- Problem #42 Coded triangle numbers || solutions
- Problem #43 Sub-string divisibility || solutions
- Problem #44 Pentagon numbers || solutions
- Problem #45 Triangular, pentagonal, and hexagonal || solutions
- Problem #46 Goldbach's other conjecture || solutions
- Problem #47 Distinct primes factors || solutions
- Problem #48 Self powers || solutions
- Problem #49 Prime permutations || solutions
- Problem #50 Consecutive prime sum || solutions
- Problem #51 Prime digit replacements || solutions
- Problem #52 Permuted multiples || solutions
- Problem #53 Combinatoric selections || solutions
- Problem #54 Poker hands || solutions
- Problem #55 Lychrel numbers || solutions
- Problem #56 Powerful digit sum || solutions
- Problem #57 Square root convergents || solutions
- Problem #58 Spiral primes || solutions
- Problem #59 XOR decryption || solutions
- Problem #60 Prime pair sets || solutions
- Problem #61 Cyclical figurate numbers || solutions
- Problem #62 Cubic permutations || solutions
- Problem #63 Powerful digit counts || solutions
- Problem #64 Odd period square roots || solutions
- Problem #65 Convergents of e || solutions
- Problem #66 Diophantine equation || solutions
- Problem #67 Maximum path sum II || solutions
- Problem #68 Magic 5-gon ring || solutions
- Problem #69 Totient maximum || solutions
- Problem #70 Totient permutation || solutions
- Problem #71 Ordered fractions || solutions
- Problem #72 Counting fractions || solutions
- Problem #73 Counting fractions in a range || solutions
- Problem #74 Digit factorial chains || solutions
- Problem #75 Singular integer right triangles || solutions
- Problem #76 Counting summations || solutions
- Problem #77 Prime summations || solutions
- Problem #78 Coin partitions || solutions
- Problem #79 Passcode derivation || solutions
- Problem #80 Square root digital expansion || solutions
- Problem #81 Path sum: two ways || solutions
- Problem #82 Path sum: three ways || solutions
- Problem #83 Path sum: four ways || solutions
- Problem #84 Monopoly odds || solutions
- Problem #85 Counting rectangles || solutions
- Problem #86 Cuboid route || solutions
- Problem #87 Prime power triples || solutions
- Problem #88 Product-sum numbers || solutions
- Problem #89 Roman numerals || solutions
- Problem #90 Cube digit pairs || solutions
- Problem #91 Right triangles with integer coordinates || solutions
- Problem #92 Square digit chains || solutions
- Problem #93 Arithmetic expressions || solutions
- Problem #94 Almost equilateral triangles || solutions
- Problem #95 Amicable chains || solutions
- Problem #96 Su Doku || solutions
- Problem #97 Large non-Mersenne prime || solutions
- Problem #98 Anagramic squares || solutions
- Problem #99 Largest exponential || solutions
- Problem #100 Arranged probability || solutions
- Problem #101 Optimum polynomial || solutions
- Problem #102 Triangle containment || solutions
- Problem #103 Special subset sums: optimum || solutions
- Problem #104 Pandigital Fibonacci ends || solutions
- Problem #105 Special subset sums: testing || solutions
- Problem #106 Special subset sums: meta-testing || solutions
- Problem #107 Minimal network || solutions
- Problem #108 Diophantine reciprocals I || solutions
- Problem #109 Darts || solutions
- Problem #110 Diophantine reciprocals II || solutions
- Problem #111 Primes with runs || solutions
- Problem #112 Bouncy numbers || solutions
- Problem #113 Non-bouncy numbers || solutions
- Problem #114 Counting block combinations I || solutions
- Problem #115 Counting block combinations II || solutions
- Problem #116 Red, green or blue tiles || solutions
- Problem #117 Red, green, and blue tiles || solutions
- Problem #118 Pandigital prime sets || solutions
- Problem #119 Digit power sum || solutions
- Problem #120 Square remainders || solutions
- Problem #121 Disc game prize fund || solutions
- Problem #122 Efficient exponentiation || solutions
- Problem #123 Prime square remainders || solutions
- Problem #124 Ordered radicals || solutions
- Problem #125 Palindromic sums || solutions
- Problem #126 Cuboid layers || solutions
- Problem #127 abc-hits || solutions
- Problem #128 Hexagonal tile differences || solutions
- Problem #129 Repunit divisibility || solutions
- Problem #130 Composites with prime repunit property || solutions
- Problem #131 Prime cube partnership || solutions
- Problem #132 Large repunit factors || solutions
- Problem #133 Repunit nonfactors || solutions
- Problem #134 Prime pair connection || solutions
- Problem #135 Same differences || solutions
- Problem #136 Singleton difference || solutions
- Problem #137 Fibonacci golden nuggets || solutions
- Problem #138 Special isosceles triangles || solutions
- Problem #139 Pythagorean tiles || solutions
- Problem #140 Modified Fibonacci golden nuggets || solutions
- Problem #141 Investigating progressive numbers, n, which are also square || solutions
- Problem #142 Perfect Square Collection || solutions
- Problem #143 Investigating the Torricelli point of a triangle || solutions
- Problem #144 Investigating multiple reflections of a laser beam || solutions
- Problem #145 How many reversible numbers are there below one-billion? || solutions
- Problem #146 Investigating a Prime Pattern || solutions
- Problem #147 Rectangles in cross-hatched grids || solutions
- Problem #148 Exploring Pascal's triangle || solutions
- Problem #149 Searching for a maximum-sum subsequence || solutions
- Problem #150 Searching a triangular array for a sub-triangle having minimum-sum || solutions
- Problem #151 Paper sheets of standard sizes: an expected-value problem || solutions
- Problem #152 Writing 1/2 as a sum of inverse squares || solutions
- Problem #153 Investigating Gaussian Integers || solutions
- Problem #154 Exploring Pascal's pyramid || solutions
- Problem #155 Counting Capacitor Circuits || solutions
- Problem #156 Counting Digits || solutions
- Problem #157 Solving the diophantine equation 1/a+1/b= p/10n || solutions
- Problem #158 Exploring strings for which only one character comes lexicographically after its neighbour to the left || solutions
- Problem #159 Digital root sums of factorisations || solutions
- Problem #160 Factorial trailing digits || solutions
- Problem #161 Triominoes || solutions
- Problem #162 Hexadecimal numbers || solutions
- Problem #163 Cross-hatched triangles || solutions
- Problem #164 Numbers for which no three consecutive digits have a sum greater than a given value || solutions
- Problem #165 Intersections || solutions
- Problem #166 Criss Cross || solutions
- Problem #167 Investigating Ulam sequences || solutions
- Problem #168 Number Rotations || solutions
- Problem #169 Exploring the number of different ways a number can be expressed as a sum of powers of 2 || solutions
- Problem #170 Find the largest 0 to 9 pandigital that can be formed by concatenating products || solutions
- Problem #171 Finding numbers for which the sum of the squares of the digits is a square || solutions
- Problem #172 Investigating numbers with few repeated digits || solutions
- Problem #173 Using up to one million tiles how many different "hollow" square laminae can be formed? || solutions
- Problem #174 Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements || solutions
- Problem #175 Fractions involving the number of different ways a number can be expressed as a sum of powers of 2 || solutions
- Problem #176 Right-angled triangles that share a cathetus || solutions
- Problem #177 Integer angled Quadrilaterals || solutions
- Problem #178 Step Numbers || solutions
- Problem #179 Consecutive positive divisors || solutions
- Problem #180 Rational zeros of a function of three variables || solutions
- Problem #181 Investigating in how many ways objects of two different colours can be grouped || solutions
- Problem #182 RSA encryption || solutions
- Problem #183 Maximum product of parts || solutions
- Problem #184 Triangles containing the origin || solutions
- Problem #185 Number Mind || solutions
- Problem #186 Connectedness of a network || solutions
- Problem #187 Semiprimes || solutions
- Problem #188 The hyperexponentiation of a number || solutions
- Problem #189 Tri-colouring a triangular grid || solutions
- Problem #190 Maximising a weighted product || solutions
- Problem #191 Prize Strings || solutions
- Problem #192 Best Approximations || solutions
- Problem #193 Squarefree Numbers || solutions
- Problem #194 Coloured Configurations || solutions
- Problem #195 Inscribed circles of triangles with one angle of 60 degrees || solutions
- Problem #196 Prime triplets || solutions
- Problem #197 Investigating the behaviour of a recursively defined sequence || solutions
- Problem #198 Ambiguous Numbers || solutions
- Problem #199 Iterative Circle Packing || solutions
- Problem #200 Find the 200th prime-proof sqube containing the contiguous sub-string "200" || solutions
- Problem #201 Subsets with a unique sum || solutions
- Problem #202 Laserbeam || solutions
- Problem #203 Squarefree Binomial Coefficients || solutions
- Problem #204 Generalised Hamming Numbers || solutions
- Problem #205 Dice Game || solutions
- Problem #206 Concealed Square || solutions
- Problem #207 Integer partition equations || solutions
- Problem #208 Robot Walks || solutions
- Problem #209 Circular Logic || solutions
- Problem #210 Obtuse Angled Triangles || solutions
- Problem #211 Divisor Square Sum || solutions
- Problem #212 Combined Volume of Cuboids || solutions
- Problem #213 Flea Circus || solutions
- Problem #214 Totient Chains || solutions
- Problem #215 Crack-free Walls || solutions
- Problem #216 Investigating the primality of numbers of the form 2n2-1 || solutions
- Problem #217 Balanced Numbers || solutions
- Problem #218 Perfect right-angled triangles || solutions
- Problem #219 Skew-cost coding || solutions
- Problem #220 Heighway Dragon || solutions
- Problem #221 Alexandrian Integers || solutions
- Problem #222 Sphere Packing || solutions
- Problem #223 Almost right-angled triangles I || solutions
- Problem #224 Almost right-angled triangles II || solutions
- Problem #225 Tribonacci non-divisors || solutions
- Problem #226 A Scoop of Blancmange || solutions
- Problem #227 The Chase || solutions
- Problem #228 Minkowski Sums || solutions
- Problem #229 Four Representations using Squares || solutions
- Problem #230 Fibonacci Words || solutions
- Problem #231 The prime factorisation of binomial coefficients || solutions
- Problem #232 The Race || solutions
- Problem #233 Lattice points on a circle || solutions
- Problem #234 Semidivisible numbers || solutions
- Problem #235 An Arithmetic Geometric sequence || solutions
- Problem #236 Luxury Hampers || solutions
- Problem #237 Tours on a 4 x n playing board || solutions
- Problem #238 Infinite string tour || solutions
- Problem #239 Twenty-two Foolish Primes || solutions
- Problem #240 Top Dice || solutions
- Problem #241 Perfection Quotients || solutions
- Problem #242 Odd Triplets || solutions
- Problem #243 Resilience || solutions
- Problem #244 Sliders || solutions
- Problem #245 Coresilience || solutions
- Problem #246 Tangents to an ellipse || solutions
- Problem #247 Squares under a hyperbola || solutions
- Problem #248 Numbers for which Euler’s totient function equals 13! || solutions
- Problem #249 Prime Subset Sums || solutions
- Problem #250 250250 || solutions
- Problem #251 Cardano Triplets || solutions
- Problem #252 Convex Holes || solutions
- Problem #253 Tidying up || solutions
- Problem #254 Sums of Digit Factorials || solutions
- Problem #255 Rounded Square Roots || solutions
- Problem #256 Tatami-Free Rooms || solutions
- Problem #257 Angular Bisectors || solutions
- Problem #258 A lagged Fibonacci sequence || solutions
- Problem #259 Reachable Numbers || solutions
- Problem #260 Stone Game || solutions
- Problem #261 Pivotal Square Sums || solutions
- Problem #262 Mountain Range || solutions
- Problem #263 An engineers' dream come true || solutions
- Problem #264 Triangle Centres || solutions
- Problem #265 Binary Circles || solutions
- Problem #266 Pseudo Square Root || solutions
- Problem #267 Billionaire || solutions
- Problem #268 Counting numbers with at least four distinct prime factors less than 100 || solutions
- Problem #269 Polynomials with at least one integer root || solutions
- Problem #270 Cutting Squares || solutions
- Problem #271 Modular Cubes, part 1 || solutions
- Problem #272 Modular Cubes, part 2 || solutions
- Problem #273 Sum of Squares || solutions
- Problem #274 Divisibility Multipliers || solutions
- Problem #275 Balanced Sculptures || solutions
- Problem #276 Primitive Triangles || solutions
- Problem #277 A Modified Collatz sequence || solutions
- Problem #278 Linear Combinations of Semiprimes || solutions
- Problem #279 Triangles with integral sides and an integral angle || solutions
- Problem #280 Ant and seeds || solutions
- Problem #281 Pizza Toppings || solutions
- Problem #282 The Ackermann function || solutions
- Problem #283 Integer sided triangles for which the area/perimeter ratio is integral || solutions
- Problem #284 Steady Squares || solutions
- Problem #285 Pythagorean odds || solutions
- Problem #286 Scoring probabilities || solutions
- Problem #287 Quadtree encoding (a simple compression algorithm) || solutions
- Problem #288 An enormous factorial || solutions
- Problem #289 Eulerian Cycles || solutions
- Problem #290 Digital Signature || solutions
- Problem #291 Panaitopol Primes || solutions
- Problem #292 Pythagorean Polygons || solutions
- Problem #293 Pseudo-Fortunate Numbers || solutions
- Problem #294 Sum of digits - experience #23 || solutions
- Problem #295 Lenticular holes || solutions
- Problem #296 Angular Bisector and Tangent || solutions
- Problem #297 Zeckendorf Representation || solutions
- Problem #298 Selective Amnesia || solutions
- Problem #299 Three similar triangles || solutions
- Problem #300 Protein folding || solutions
- Problem #301 Nim || solutions
- Problem #302 Strong Achilles Numbers || solutions
- Problem #303 Multiples with small digits || solutions
- Problem #304 Primonacci || solutions
- Problem #305 Reflexive Position || solutions
- Problem #306 Paper-strip Game || solutions
- Problem #307 Chip Defects || solutions
- Problem #308 An amazing Prime-generating Automaton || solutions
- Problem #309 Integer Ladders || solutions
- Problem #310 Nim Square || solutions
- Problem #311 Biclinic Integral Quadrilaterals || solutions
- Problem #312 Cyclic paths on Sierpiński graphs || solutions
- Problem #313 Sliding game || solutions
- Problem #314 The Mouse on the Moon || solutions
- Problem #315 Digital root clocks || solutions
- Problem #316 Numbers in decimal expansions || solutions
- Problem #317 Firecracker || solutions
- Problem #318 2011 nines || solutions
- Problem #319 Bounded Sequences || solutions
- Problem #320 Factorials divisible by a huge integer || solutions
- Problem #321 Swapping Counters || solutions
- Problem #322 Binomial coefficients divisible by 10 || solutions
- Problem #323 Bitwise-OR operations on random integers || solutions
- Problem #324 Building a tower || solutions
- Problem #325 Stone Game II || solutions
- Problem #326 Modulo Summations || solutions
- Problem #327 Rooms of Doom || solutions
- Problem #328 Lowest-cost Search || solutions
- Problem #329 Prime Frog || solutions
- Problem #330 Euler's Number || solutions
- Problem #331 Cross flips || solutions
- Problem #332 Spherical triangles || solutions
- Problem #333 Special partitions || solutions
- Problem #334 Spilling the beans || solutions
- Problem #335 Gathering the beans || solutions
- Problem #336 Maximix Arrangements || solutions
- Problem #337 Totient Stairstep Sequences || solutions
- Problem #338 Cutting Rectangular Grid Paper || solutions
- Problem #339 Peredur fab Efrawg || solutions
- Problem #340 Crazy Function || solutions
- Problem #341 Golomb's self-describing sequence || solutions
- Problem #342 The totient of a square is a cube || solutions
- Problem #343 Fractional Sequences || solutions
- Problem #344 Silver dollar game || solutions
- Problem #345 Matrix Sum || solutions
- Problem #346 Strong Repunits || solutions
- Problem #347 Largest integer divisible by two primes || solutions
- Problem #348 Sum of a square and a cube || solutions
- Problem #349 Langton's ant || solutions
- Problem #350 Constraining the least greatest and the greatest least || solutions
- Problem #351 Hexagonal orchards || solutions
- Problem #352 Blood tests || solutions
- Problem #353 Risky moon || solutions
- Problem #354 Distances in a bee's honeycomb || solutions
- Problem #355 Maximal coprime subset || solutions
- Problem #356 Largest roots of cubic polynomials || solutions
- Problem #357 Prime generating integers || solutions
- Problem #358 Cyclic numbers || solutions
- Problem #359 Hilbert's New Hotel || solutions
- Problem #360 Scary Sphere || solutions
- Problem #361 Subsequence of Thue-Morse sequence || solutions
- Problem #362 Squarefree factors || solutions
- Problem #363 Bézier Curves || solutions
- Problem #364 Comfortable distance || solutions
- Problem #365 A huge binomial coefficient || solutions
- Problem #366 Stone Game III || solutions
- Problem #367 Bozo sort || solutions
- Problem #368 A Kempner-like series || solutions
- Problem #369 Badugi || solutions
- Problem #370 Geometric triangles || solutions
- Problem #371 Licence plates || solutions
- Problem #372 Pencils of rays || solutions
- Problem #373 Circumscribed Circles || solutions
- Problem #374 Maximum Integer Partition Product || solutions
- Problem #375 Minimum of subsequences || solutions
- Problem #376 Nontransitive sets of dice || solutions
- Problem #377 Sum of digits, experience 13 || solutions
- Problem #378 Triangle Triples || solutions
- Problem #379 Least common multiple count || solutions
- Problem #380 Amazing Mazes! || solutions
- Problem #381 (prime-k) factorial || solutions
- Problem #382 Generating polygons || solutions
- Problem #383 Divisibility comparison between factorials || solutions
- Problem #384 Rudin-Shapiro sequence || solutions
- Problem #385 Ellipses inside triangles || solutions
- Problem #386 Maximum length of an antichain || solutions
- Problem #387 Harshad Numbers || solutions
- Problem #388 Distinct Lines || solutions
- Problem #389 Platonic Dice || solutions
- Problem #390 Triangles with non rational sides and integral area || solutions
- Problem #391 Hopping Game || solutions
- Problem #392 Enmeshed unit circle || solutions
- Problem #393 Migrating ants || solutions
- Problem #394 Eating pie || solutions
- Problem #395 Pythagorean tree || solutions
- Problem #396 Weak Goodstein sequence || solutions
- Problem #397 Triangle on parabola || solutions
- Problem #398 Cutting rope || solutions
- Problem #399 Squarefree Fibonacci Numbers || solutions
- Problem #400 Fibonacci tree game || solutions
- Problem #401 Sum of squares of divisors || solutions
- Problem #402 Integer-valued polynomials || solutions
- Problem #403 Lattice points enclosed by parabola and line || solutions
- Problem #404 Crisscross Ellipses || solutions
- Problem #405 A rectangular tiling || solutions
- Problem #406 Guessing Game || solutions
- Problem #407 Idempotents || solutions
- Problem #408 Admissible paths through a grid || solutions
- Problem #409 Nim Extreme || solutions
- Problem #410 Circle and tangent line || solutions
- Problem #411 Uphill paths || solutions
- Problem #412 Gnomon numbering || solutions
- Problem #413 One-child Numbers || solutions
- Problem #414 Kaprekar constant || solutions
- Problem #415 Titanic sets || solutions
- Problem #416 A frog's trip || solutions
- Problem #417 Reciprocal cycles II || solutions
- Problem #418 Factorisation triples || solutions
- Problem #419 Look and say sequence || solutions
- Problem #420 2x2 positive integer matrix || solutions
- Problem #421 Prime factors of n15+1 || solutions
- Problem #422 Sequence of points on a hyperbola || solutions
- Problem #423 Consecutive die throws || solutions
- Problem #424 Kakuro || solutions
- Problem #425 Prime connection || solutions
- Problem #426 Box-ball system || solutions
- Problem #427 n-sequences || solutions
- Problem #428 Necklace of circles || solutions
- Problem #429 Sum of squares of unitary divisors || solutions
- Problem #430 Range flips || solutions
- Problem #431 Square Space Silo || solutions
- Problem #432 Totient sum || solutions
- Problem #433 Steps in Euclid's algorithm || solutions
- Problem #434 Rigid graphs || solutions
- Problem #435 Polynomials of Fibonacci numbers || solutions
- Problem #436 Unfair wager || solutions
- Problem #437 Fibonacci primitive roots || solutions
- Problem #438 Integer part of polynomial equation's solutions || solutions
- Problem #439 Sum of sum of divisors || solutions
- Problem #440 GCD and Tiling || solutions
- Problem #441 The inverse summation of coprime couples || solutions
- Problem #442 Eleven-free integers || solutions
- Problem #443 GCD sequence || solutions
- Problem #444 The Roundtable Lottery || solutions
- Problem #445 Retractions A || solutions
- Problem #446 Retractions B || solutions
- Problem #447 Retractions C || solutions
- Problem #448 Average least common multiple || solutions
- Problem #449 Chocolate covered candy || solutions
- Problem #450 Hypocycloid and Lattice points || solutions
- Problem #451 Modular inverses || solutions
- Problem #452 Long Products || solutions
- Problem #453 Lattice Quadrilaterals || solutions
- Problem #454 Diophantine reciprocals III || solutions
- Problem #455 Powers With Trailing Digits || solutions
- Problem #456 Triangles containing the origin II || solutions
- Problem #457 A polynomial modulo the square of a prime || solutions
- Problem #458 Permutations of Project || solutions
- Problem #459 Flipping game || solutions
- Problem #460 An ant on the move || solutions
- Problem #461 Almost Pi || solutions
- Problem #462 Permutation of 3-smooth numbers || solutions
- Problem #463 A weird recurrence relation || solutions
- Problem #464 Möbius function and intervals || solutions
- Problem #465 Polar polygons || solutions
- Problem #466 Distinct terms in a multiplication table || solutions
- Problem #467 Superinteger || solutions
- Problem #468 Smooth divisors of binomial coefficients || solutions
- Problem #469 Empty chairs || solutions
- Problem #470 Super Ramvok || solutions
- Problem #471 Triangle inscribed in ellipse || solutions
- Problem #472 Comfortable Distance II || solutions
- Problem #473 Phigital number base || solutions
- Problem #474 Last digits of divisors || solutions
- Problem #475 Music festival || solutions
- Problem #476 Circle Packing II || solutions
- Problem #477 Number Sequence Game || solutions
- Problem #478 Mixtures || solutions
- Problem #479 Roots on the Rise || solutions
- Problem #480 The Last Question || solutions
- Problem #481 Chef Showdown || solutions
- Problem #482 The incenter of a triangle || solutions
- Problem #483 Repeated permutation || solutions
- Problem #484 Arithmetic Derivative || solutions
- Problem #485 Maximum number of divisors || solutions
- Problem #486 Palindrome-containing strings || solutions
- Problem #487 Sums of power sums || solutions
- Problem #488 Unbalanced Nim || solutions
- Problem #489 Common factors between two sequences || solutions
- Problem #490 Jumping frog || solutions
- Problem #491 Double pandigital number divisible by 11 || solutions
- Problem #492 Exploding sequence || solutions
- Problem #493 Under The Rainbow || solutions
- Problem #494 Collatz prefix families || solutions
- Problem #495 Writing n as the product of k distinct positive integers || solutions
- Problem #496 Incenter and circumcenter of triangle || solutions
- Problem #497 Drunken Tower of Hanoi || solutions
- Problem #498 Remainder of polynomial division || solutions
- Problem #499 St. Petersburg Lottery || solutions
- Problem #500 Problem 500!!! || solutions
- Problem #501 Eight Divisors || solutions
- Problem #502 Counting Castles || solutions
- Problem #503 Compromise or persist || solutions
- Problem #504 Square on the Inside || solutions
- Problem #505 Bidirectional Recurrence || solutions
- Problem #506 Clock sequence || solutions
- Problem #507 Shortest Lattice Vector || solutions
- Problem #508 Integers in base i-1 || solutions
- Problem #509 Divisor Nim || solutions
- Problem #510 Tangent Circles || solutions
- Problem #511 Sequences with nice divisibility properties || solutions
- Problem #512 Sums of totients of powers || solutions
- Problem #513 Integral median || solutions
- Problem #514 Geoboard Shapes || solutions
- Problem #515 Dissonant Numbers || solutions
- Problem #516 5-smooth totients || solutions
- Problem #517 A real recursion || solutions
- Problem #518 Prime triples and geometric sequences || solutions
- Problem #519 Tricolored Coin Fountains || solutions
- Problem #520 Simbers || solutions
- Problem #521 Smallest prime factor || solutions
- Problem #522 Hilbert's Blackout || solutions
- Problem #523 First Sort I || solutions
- Problem #524 First Sort II || solutions
- Problem #525 Rolling Ellipse || solutions
- Problem #526 Largest prime factors of consecutive numbers || solutions
- Problem #527 Randomized Binary Search || solutions
- Problem #528 Constrained Sums || solutions
- Problem #529 10-substrings || solutions
- Problem #530 GCD of Divisors || solutions
- Problem #531 Chinese leftovers || solutions
- Problem #532 Nanobots on Geodesics || solutions
- Problem #533 Minimum values of the Carmichael function || solutions
- Problem #534 Weak Queens || solutions
- Problem #535 Fractal Sequence || solutions
- Problem #536 Modulo power identity || solutions
- Problem #537 Counting tuples || solutions
- Problem #538 Maximum quadrilaterals || solutions
- Problem #539 Odd elimination || solutions
- Problem #540 Counting primitive Pythagorean triples || solutions
- Problem #541 Divisibility of Harmonic Number Denominators || solutions
- Problem #542 Geometric Progression with Maximum Sum || solutions
- Problem #543 Prime-Sum Numbers || solutions
- Problem #544 Chromatic Conundrum || solutions
- Problem #545 Faulhaber's Formulas || solutions
- Problem #546 The Floor's Revenge || solutions
- Problem #547 Distance of random points within hollow square laminae || solutions
- Problem #548 Gozinta Chains || solutions
- Problem #549 Divisibility of factorials || solutions
- Problem #550 Divisor game || solutions
- Problem #551 Sum of digits sequence || solutions
- Problem #552 Chinese leftovers II || solutions
- Problem #553 Power sets of power sets || solutions
- Problem #554 Centaurs on a chess board || solutions
- Problem #555 McCarthy 91 function || solutions
- Problem #556 Squarefree Gaussian Integers || solutions
- Problem #557 Cutting triangles || solutions
- Problem #558 Irrational base || solutions
- Problem #559 Permuted Matrices || solutions
- Problem #560 Coprime Nim || solutions
- Problem #561 Divisor Pairs || solutions
- Problem #562 Maximal perimeter || solutions
- Problem #563 Robot Welders || solutions
- Problem #564 Maximal polygons || solutions
- Problem #565 Divisibility of sum of divisors || solutions
- Problem #566 Cake Icing Puzzle || solutions
- Problem #567 Reciprocal games I || solutions
- Problem #568 Reciprocal games II || solutions
- Problem #569 Prime Mountain Range || solutions
- Problem #570 Snowflakes || solutions
- Problem #571 Super Pandigital Numbers || solutions
- Problem #572 Idempotent matrices || solutions
- Problem #573 Unfair race || solutions
- Problem #574 Verifying Primes || solutions
- Problem #575 Wandering Robots || solutions
- Problem #576 Irrational jumps || solutions
- Problem #577 Counting hexagons || solutions
- Problem #578 Integers with decreasing prime powers || solutions
- Problem #579 Lattice points in lattice cubes || solutions
- Problem #580 Squarefree Hilbert numbers || solutions
- Problem #581 47-smooth triangular numbers || solutions
- Problem #582 Nearly isosceles 120 degree triangles || solutions
- Problem #583 Heron Envelopes || solutions
- Problem #584 Birthday Problem Revisited || solutions
- Problem #585 Nested square roots || solutions
- Problem #586 Binary Quadratic Form || solutions
- Problem #587 Concave triangle || solutions
- Problem #588 Quintinomial coefficients || solutions
- Problem #589 Poohsticks Marathon || solutions
- Problem #590 Sets with a given Least Common Multiple || solutions
- Problem #591 Best Approximations by Quadratic Integers || solutions
- Problem #592 Factorial trailing digits 2 || solutions
- Problem #593 Fleeting Medians || solutions
- Problem #594 Rhombus Tilings || solutions
- Problem #595 Incremental Random Sort || solutions
- Problem #596 Number of lattice points in a hyperball || solutions
- Problem #597 Torpids || solutions
- Problem #598 Split Divisibilities || solutions
- Problem #599 Distinct Colourings of a Rubik's Cube || solutions
- Problem #600 Integer sided equiangular hexagons || solutions
- Problem #601 Divisibility streaks || solutions
- Problem #602 Product of Head Counts || solutions