euler7.hs

euler7 = primes !! 10000

primes = 2 : 3 : [x| x <- [5, 7..], is_prime x]

is_prime n = is_prime' [3, 5..]
  where
    is_prime' (x : xs)
      | n `mod` x == 0  = False
      | x ^ 2 > n       = True
      | otherwise       = is_prime' xs