#lang racket

(define (invfact x i)
  (define y (/ x i))
  (cond
    [(= y 1) x]
    [(> y 1) (invfact y (+ i 1))]
    [(< y 1) (error "Aucune factorielle possible")]))

(define (display_invfact n)
  (printf "~a = ~a!\n" n (invfact n 2)))

(display_invfact 120)
(display_invfact 3628800)
(display_invfact 479001600)
(display_invfact 6)
(display_invfact 18)