Project Euler No. 3

Problem

The prime factors of $13195$ are $5$, $7$, $13$ and $29$.

What is the largest prime factor of the number $600851475143$ ?

Haskell Code

Euler_003.hs

module Main where
import Data.List

-- (x:xs)は自然数の列で、小さい方からnを除算をしていく。
-- 剰余が0ならもう一度その同じ数で除算し、
-- そうでないなら次の自然数で除算するという再帰。

factoring n fs (x:xs)
  | n == 1 = fs
  | (mod n x == 0) = factoring (div n x) (x:fs) (x:xs)
  |otherwise = factoring n fs xs

main = print answer
  where 
    answer = maximum $ factoring n [] [2..n]
    n = 600851475143

Answer

6**7