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Problem 3¶

#!r6rs
#!chezscheme

(import (chezscheme))

(define answer-3
  (let* ((n 600851475143)
         (check-max (isqrt n)))
    (let loop ((current 3) (rest n) (max-prime 1))
      (cond
        [(< check-max current) max-prime]
        [(zero? (mod rest current))
         (loop current (div rest current) current)]
        [else (loop (+ current 2) rest max-prime)]))))

(printf "3: ~D~%" answer-3)