import Data.List
import Data.Ratio

bernoulli 0 = 1
bernoulli n | n`mod`2 > 0 && n > 1 = 0%1
bernoulli n | n>0 =  subber n (n-1)
    where
        subber a (-1) = 0
        subber a b  =  a `choos` b % (b-n-1)* bernoulli b + subber a (b-1)
n `choos` k = product [n-k+1..n] `div` product [1..k]