-- derived from
-- https://stackoverflow.com/questions/17892313/
--  sieve-of-eratosthenes-with-wheel-factorization/17892352#17892352

euler limit = ([2,3,5,7] ++) . g
                           . takeWhile (<= limit) . scanl (+) 11
                           . tail . cycle . (zipWith (-) =<< tail)
                           $ [x | x <- [1..211], gcd x 210 == 1]
      where
      g xs@(x:ys) | x*x > limit = xs
                  | otherwise   = x : g (remMultsOf x ys)
                        --      = x : g (remove (multsOf x xs) ys)
                        -- where
                        --    multsOf x xs = map (x*) xs    -OR-   = \y -> rem y x == 0
                        --    remove xs ys = ys \\ xs       -OR-   = filter (not . xs) ys
                                            -- (\\) = Data.List.Ordered.minus
      remMultsOf x ys = r (x*x) ys ys
         where
         r m xs []                = []
         r m xs (h:t) | m == h    =     r (x*head xs) (tail xs)  t
                      | otherwise = h : r   m               xs   t