Exploring the Hailstone Sequence in Clojure. See https://en.wikipedia.org/wiki/HOTPO

hailstone.clj

(defn hotpo
  "One iteration of the hailstone sequence."
  [n]
  (if (even? n)
    (/ n 2)
    (inc (* 3 n))))

(defn hotpot [x]
  "Finds a hailstone sequence starting with integer x."
  (take-while #(> % 1)
              (iterate hotpo x)))

(defn hotpotato
  "Returns the length of a hailstone sequence starting with integer x."
  [x]
  (count (hotpot x)))

(defn hottest-potato
  "Finds the longest hailstone sequence starting with an integer less than y."
  [y]
  (apply max-key hotpotato (range y)))