Data commit

Task/Weird-numbers/Racket/weird-numbers.rkt

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+#lang racket
+
+(require math/number-theory)
+
+(define (abundant? n proper-divisors)
+  (> (apply + proper-divisors) n))
+
+(define (semi-perfect? n proper-divisors)
+    (let recur ((ds proper-divisors) (n n))
+      (or (zero? n)
+          (and (positive? n)
+               (pair? ds)
+               (or (recur (cdr ds) n)
+                   (recur (cdr ds) (- n (car ds))))))))
+
+(define (weird? n)
+  (let ((proper-divisors (drop-right (divisors n) 1))) ;; divisors includes n
+    (and (abundant? n proper-divisors) (not (semi-perfect? n proper-divisors)))))
+
+(module+ main
+  (let recur ((i 0) (n 1) (acc null))
+    (cond [(= i 25) (reverse acc)]
+          [(weird? n) (recur (add1 i) (add1 n) (cons n acc))]
+          [else (recur i (add1 n) acc)])))
+
+(module+ test
+  (require rackunit)
+  (check-true (weird? 70))
+  (check-false (weird? 12)))