clojure happy number http://www.4clojure.com/problem/86

happy-numbers.clj

(defn happy-numbers
  [n]
  (letfn [(next-happy [n]
            (->> (str n)
                 (partition 1 1)
                 (map first)
                 (take-while #(not (= \. %)))
                 (map (comp #(Math/pow % 2) read-string str))
                 (reduce +)))
          (repeats? [coll]
            (->> coll
                 frequencies
                 (filter #(< 1 (second %)))
                 ((complement empty?))))]
    (->> (iterate inc 1)
         (map #(take % (iterate next-happy n)))
         (drop-while #(not (or (== 1 (last %)) (repeats? %))))
         first
         (#(if (== 1 (last %)) true false)))))