ENH euler 7

Author: eigenfoo

euler007.hs

@@ -0,0 +1,10 @@
+main = print $ primes !! 10000 -- zero indexing; 10001st prime
+  where primes = 2 : filter (\n -> (length $ prime_factors n) == 1) [3,5..]
+
+prime_factors :: (Integral a) => a -> [a]
+prime_factors 1 = []
+prime_factors n
+  | factor == [] = [n]
+  | n < (head factor)^2 = [n]   -- stop searching if sqrt n < head factor
+  | otherwise = factor ++ prime_factors (n `div` (head factor))
+    where factor = take 1 [x | x <- [2..n-1], n `rem` x == 0]