1 files changed, 24 insertions, 0 deletions
diff --git a/coding-exercises/1/27.rkt b/coding-exercises/1/27.rkt
new file mode 100644
index 0000000..8762d6c
--- /dev/null
+++ b/coding-exercises/1/27.rkt
@@ -0,0 +1,24 @@
+#lang racket
+(require sicp)
+
+(define (square x)
+  (* x x))
+
+(define (expmod base e m)
+  (cond 
+    ((= e 0) 1)
+    ((even? e)
+     (remainder (square (expmod base (/ e 2) m)) m))
+    (else
+      (remainder (* base (expmod base (- e 1) m)) m))))
+
+(define (fermat? a n)
+  (= (expmod a n n) a))
+
+(define (all-fermat n)
+  (define (f a n)
+      (cond
+        ((= a 0) true)
+        ((fermat? (- a 1) n) (f (- a 1) n))
+        (else false)))
+  (f n n))