0012.highly_divisible_triangular_number.R

# The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:
  
# 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

# Let us list the factors of the first seven triangle numbers:
#   
# 1: 1
# 3: 1,3
# 6: 1,2,3,6
# 10: 1,2,5,10
# 15: 1,3,5,15
# 21: 1,3,7,21
# 28: 1,2,4,7,14,28
# We can see that 28 is the first triangle number to have over five divisors.
# 
# What is the value of the first triangle number to have over five hundred divisors?


factors <- function(x) {
  potential_factors = 1:ceiling(x/2)
  factors = potential_factors[x %% potential_factors == 0]
  length(factors)
}



test <- purrr::map(100000:1000000, factors) %>% unlist()

# This takes RIDICULOUSLY LONG....
test[test > 500]