; The prime factors of 13195 are 5, 7, 13 and 29.
; What is the largest prime factor of the number 600851475143 ?
; is a a multiple of n?
(defn div-up [n, d]
  (/ (+ n (dec d)) d))
(defn multiple? [n, a]
  (zero? (mod n a)))
(defn factors [n]
  (filter (partial multiple? n) (range 2 (div-up n 2))))
(defn prime? [n]
  (empty? (factors n)))
(let [n 600851475143]
  (println
    (time (last (doall (filter prime? (factors n)))))
    (time (doall (filter prime? (factors n))))
    (time (doall (factors n)))))

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