ex1.21.rkt

#lang scheme
;; Exercise 1.21
;; Use the smallest-divisor procedure to find the smallest divisor of
;; each of the following numbers: 199, 1999, 19999.

(define (smallest-divisor n)
  (find-divisor n 2))

(define (find-divisor n test-divisor)
  (cond
   ((> (square test-divisor) n) n)
   ((divides? test-divisor n) test-divisor)
   (else (find-divisor n (+ test-divisor 1)))))

(define (divides? a b)
  (= (remainder b a) 0))

(define (square x) (* x x))