Initial data commit

Task/Proper-divisors/Racket/proper-divisors-1.rkt

@@ -0,0 +1,11 @@
+#lang racket
+(require math)
+(define (proper-divisors n) (drop-right (divisors n) 1))
+(for ([n (in-range 1 (add1 10))])
+  (printf "proper divisors of: ~a\t~a\n" n (proper-divisors n)))
+(define most-under-20000
+  (for/fold ([best '(1)]) ([n (in-range 2 (add1 20000))])
+    (define divs (proper-divisors n))
+    (if (< (length (cdr best)) (length divs)) (cons n divs) best)))
+(printf "~a has ~a proper divisors\n"
+        (car most-under-20000) (length (cdr most-under-20000)))

Task/Proper-divisors/Racket/proper-divisors-2.rkt

@@ -0,0 +1,38 @@
+#lang racket/base
+(provide fold-divisors ; name as per "Abundant..."
+         proper-divisors)
+
+(define (fold-divisors v n k0 kons)
+  (define n1 (add1 n))
+  (cond
+    [(>= n1 (vector-length v))
+     (define rv (make-vector n1 k0))
+     (for* ([n (in-range 1 n1)] [m (in-range (* 2 n) n1 n)])
+       (vector-set! rv m (kons n (vector-ref rv m))))
+     rv]
+    [else v]))
+
+(define proper-divisors
+  (let ([p.d-v (vector)])
+    (λ (n)
+      (set! p.d-v (reverse (fold-divisors p.d-v n null cons)))
+      (vector-ref p.d-v n))))
+
+(module+ main
+  (for ([n (in-range 1 (add1 10))])
+    (printf "proper divisors of: ~a\t~a\n" n (proper-divisors n)))
+
+  (define count-proper-divisors
+    (let ([p.d-v (vector)])
+      (λ(n) (set! p.d-v (fold-divisors p.d-v n 0 (λ (d n) (add1 n))))
+            (vector-ref p.d-v n))))
+
+  (void (count-proper-divisors 20000))
+
+  (define-values [C I]
+    (for*/fold ([C 0] [I 1])
+               ([i (in-range 1 (add1 20000))]
+                [c (in-value (count-proper-divisors i))]
+                #:when [> c C])
+      (values c i)))
+  (printf "~a has ~a proper divisors\n" I C))