Solution to Exercise 1.27:

Here is the procedure for testing whether a number is a Charmichael number:

(define (congruent? n a)
  (= (expmod a n n) a))
 
(define (carmichael? n)
  (define (iter i)
    (cond ((= i 0) #t)
          ((congruent? n i) (iter (- i 1)))
          (else #f)))
  (iter (- n 1)))

Posted by Ken Dyck in Programming