Add 1.27

sicp-ex-1.27.rkt

@@ -0,0 +1,36 @@
+#lang racket  ; needed for true / false
+
+(define (square n)
+  (* n n))
+
+(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-test n smaller-n)
+  (define (try-it a)
+    (= (expmod a n n) a))
+  (cond ((= smaller-n 1) true)
+        ((try-it smaller-n) (fermat-test n (- smaller-n 1)))
+        (else false)))
+
+(define (is-carmichael-prime? n)
+        (fermat-test n (- n 1)))
+
+561
+(is-carmichael-prime? 561)
+1105
+(is-carmichael-prime? 1105)
+1729
+(is-carmichael-prime? 1729)
+2465
+(is-carmichael-prime? 2465)
+2821
+(is-carmichael-prime? 2821)
+6601
+(is-carmichael-prime? 6601)