(define (factors n)
   (let loop ((val n) (div 2) (factors '()))
      (if (= 1 val)
         factors
         (if (= 0 (modulo val div)) 
            (loop (/ val div) div (cons div factors))
            (loop val (add1 div) factors)
         )
      )
   )
)

(define (max lst)
   (foldl (lambda (a b) (if (> a b) a b)) (car lst) (cdr lst)))

(print (max (factors 600851475143)))