carmichael.scm

(define (expmod base exp m)
  (cond ((= exp 0) 1)
	((even? exp)
	 (remainder (square (expmod base (/ exp 2) m)) m))
	(else (remainder (* base (expmod base (- exp 1) m)) m))))

(define (fermat-every n)
  (fermat-helper (- n 1) n))

(define (fermat-helper a n)
  (cond ((= a 0) #t)
        ((= (expmod a n n) a) (fermat-helper (- a 1) n))
	(else #f)))