03-euler.clj

(def sqrt [n]
  (Math/sqrt n))

(defn find-max-factor [n]
  (let [max-range (long (Math/ceil (sqrt n)))]
    (loop [i max-range]
      (if (= 0 (mod n i))
        (max i (/ n i))
        (recur (- i 1))))))

(defn find-factors
  ([n]
     (find-factors n 2N []))
  ([n divisor factors]
     (if (<= divisor n)
       (if (= 0 (mod n divisor))
         (recur (long (/ n divisor)) divisor (conj factors divisor))
         (recur n (+ divisor 1N) factors))
       factors)))

(println (apply max (find-factors 600851475143N)))