#12

highly-divisible-triangle-numbers.clj

(ns highly-divisible-triangle-numbers
  (:require [clojure.core.reducers :as r]))

(def triangles (reduce 
                (fn [x y] 
                  (conj x (+ (peek x) y))) 
                [0] 
                (range 1 20000))) 

(defn factors [n]
  (into (sorted-set)
        (reduce concat
                (for [x (range 1 (inc (Math/sqrt n))) :when (zero? (rem n x))]
                  [x (/ n x)]))))

(doseq [sol (filter #(> (count (factors %)) 500) triangles)]
  (println sol))

(count (factors 76576500))

I kind of stole the factoring code though. But really. I've written enough of those to know that I don't want to write them.