euler12.rkt

#lang racket
(define (count-divisors n [count 0] [start 1])
  (cond
   [(> start (sqrt n)) (* 2 count)]
   [(= start (sqrt n)) (+ (* 2 count) 1)]
   [(zero? (remainder n start)) (count-divisors n (+ count 1) (+ start 1))]
   [else (count-divisors n count (+ start 1))]))

(define (triangle-number n)
  (if (<= n 1)
      n
      (+ n (triangle-number (- n 1)))))

(define (euler12 [n 1])
  (if (> (count-divisors (triangle-number n)) 500)
      (triangle-number n)
      (euler12 (+ n 1))))

(println (euler12))