Data commit

Task/Emirp-primes/Scheme/emirp-primes.ss

@@ -0,0 +1,36 @@
+; Primality test by simple trial division.
+(define prime?
+  (lambda (num)
+    (if (< num 2)
+      #f
+      (let loop ((div 2))
+        (cond ((> (* div div) num) #t)
+              ((zero? (modulo num div)) #f)
+              (else (loop (1+ div))))))))
+
+; Check if number is an emirp prime.
+(define emirp?
+  (lambda (num)
+    (and (prime? num)
+         (let ((rev (string->number (list->string (reverse (string->list (number->string num)))))))
+           (and (not (= num rev)) (prime? rev))))))
+
+(printf "The first 20 emirps:")
+(do ((num 1 (1+ num)) (cnt 0))
+    ((>= cnt 20))
+  (when (emirp? num)
+    (set! cnt (1+ cnt))
+    (printf " ~d" num)))
+(newline)
+
+(printf "All emirps between 7700 and 8000:")
+(do ((num 7700 (1+ num)))
+    ((>= num 8000))
+  (when (emirp? num)
+    (printf " ~d" num)))
+(newline)
+
+(printf "The 10000th emirp: ~d~%"
+        (do ((num 1 (1+ num)) (cnt 0))
+            ((>= cnt 10000) (1- num))
+          (when (emirp? num) (set! cnt (1+ cnt)))))