1.27 Exercise 1.27

Here is a procedure to test for congruence for a number n with every integer 1 <= a <= n - 1:

(define (congruence-test num)   (define (loop current)     (cond ((= current num) #t)           ((not (= (expmod current num num) current)) #f)           (else (loop (+ current 1)))))   (loop 1))

It is trivial to verify that this procedure returns true for the given Carmichael numbers.