1 one :: Int -> Int
   2 one n = sum [x | x <- [1..n], (mod x 3 == 0 || mod x 5 == 0)]
   3 
   4 main = print $ one 999

   1 four = maximum [x | x1<-[100..999], x2<-[100..999], let x=x1*x2, let p=show x, p==reverse p]
   2 main = print $ four

   1 primes = 2 : f [3] [3,5..]
   2     where f(x:xs) ys = let (ps, qs) = span (< x^2) ys
   3                        in ps ++ f (xs ++ ps) [z | z <- qs, mod z x /= 0]
   4 main = print $ primes !! 10000

   1 ten :: Int -> Int
   2 ten n = sum primes2
   3     where primes = 2:f [3] [3,5..] where f (x:xs) ys = let (ps, qs) = span (< x^2) ys 
   4                                                        in ps ++ f (xs ++ ps) [z | z <- qs, mod z x /= 0]
   5           primes2 = takeWhile (<n) primes
   6 
   7 main = print $ ten 2000000