Data commit

Task/Smith-numbers/Racket/smith-numbers.rkt

@@ -0,0 +1,27 @@
+#lang racket
+(require math/number-theory)
+
+(define (sum-of-digits n)
+  (let inr ((n n) (s 0))
+    (if (zero? n) s (let-values (([q r] (quotient/remainder n 10))) (inr q (+ s r))))))
+
+(define (smith-number? n)
+  (and (not (prime? n))
+       (= (sum-of-digits n)
+          (for/sum ((pe (in-list (factorize n))))
+            (* (cadr pe) (sum-of-digits (car pe)))))))
+
+(module+ test
+  (require rackunit)
+  (check-equal? (sum-of-digits 0) 0)
+  (check-equal? (sum-of-digits 33) 6)
+  (check-equal? (sum-of-digits 30) 3)
+
+  (check-true (smith-number? 166)))
+
+(module+ main
+  (let loop ((ns (filter smith-number? (range 1 (add1 10000)))))
+    (unless (null? ns)
+      (let-values (([l r] (split-at ns (min (length ns) 15))))
+        (displayln l)
+        (loop r)))))