prime factors.clj

(with-test
  (defn prime-factors [n]
    ((fn this [n_ last-divisor]
      (if (= n_ 1)
        []
        (let [
            divisor
            (or
              (some
                #(when (zero? (mod n_ %)) %)
                (range last-divisor (. Math sqrt n)))
              n_)]
          (cons
            divisor
            (this (/ n_ divisor) last-divisor)))))
    n 2))
  (are (= (prime-factors _1) _2)
    1 []
    2 [2]
    3 [3]
    4 [2 2]
    5 [5]
    6 [2 3]
    7 [7]
    8 [2 2 2]
    (dec (** 2 17)) [(dec (** 2 17))]))