Data commit

Task/Partition-function-P/Racket/partition-function-p.rkt

@@ -0,0 +1,28 @@
+#lang racket
+
+(require math/number-theory)
+
+(define σ
+  (let ((memo (make-hash)))
+    (λ (z)
+      (hash-ref! memo z
+                 (λ () (apply + (divisors z)))))))
+
+(define p
+  (let ((memo (make-hash '((0 . 1)))))
+    (λ (n)
+      (hash-ref!
+       memo n
+       (λ ()
+         (let ((r (if (zero? n) 1
+             (/ (for/sum ((k (in-range (sub1 n) -1 -1)))
+                  (* (σ (- n k))
+                     (p k)))
+                n))))
+           (when (zero? (modulo n 1000)) (displayln (cons n r) (current-error-port)))
+           r))))))
+
+(map p (range 1 30))
+(p 666)
+(p 1000)
+(p 10000)