Complete Code

fatc :: Integer -> Integer
fatc n | n==0 = 1
       | n>0 = fatcauda n 1

fatcauda :: Integer -> Integer -> Integer
fatcauda n parcial | n==0 = parcial
           | n>0 = fatcauda (n-1) (n*parcial)

size :: [Int] -> Int
size []         = 0
size (head: body)   = 1 + size body

divi :: Int -> [Int]
divi n = [x | x<-[1..n], mod n x == 0]

divip :: Int -> [Int]
divip n = [x | x<-[2..n-1], mod n x == 0]

primo :: Int -> Bool
primo n | [x | x<-[2..n-1], mod n x == 0] == [] = True
    | otherwise = False

primos :: Int -> [Int]
primos n | n> 2 = [x | x<-[1..n], primo x]

multi :: Int -> Int -> [Int]
multi n i = [x*n | x<-[1..i]]

--pi :: Int -> Double
--pi n = (426880 * sqrt 10005) / divpi n

divpi :: Integer -> Double
divpi k = (((fatc (6*k)) * ((545140134*k) + 13591409))/((fatc (3*k)) * (pot (fatc k) 3) * (pot (-262537412640768000) k)))

pot :: Integer -> Integer -> Integer
pot base expo | expo == 0 = 1
              | otherwise = base * (pot base (expo-1))