Sorry, I pressed inadvertently the "send" button... The previous code has some typos... :-) The code is this: ------------------------------ isPrime :: Integer -> Bool isPrime n = isPrimeAux n 2 where -- First param is the number to be tested -- for primality. Second param the current -- divisor. isPrimeAux :: Integer -> Integer -> Bool isPrimeAux n k | fromIntegral k > sqrt (fromIntegral n) = True | otherwise = if n `mod` k == 0 then False else isPrimeAux n (k+1) main :: IO () main = print $ sum $ filter isPrime [2..1999999] ------------------------- I compiled the code with "ghc --make prob10.hs", and although it wasn't lightning fast I got the answer after a little less than a minute on my system. Hope it helped, Christos