multiplicative_persistence.hs

-- check the multiplicative persistence of a given number
-- https://www.youtube.com/watch?v=Wim9WJeDTHQ&list=PLt5AfwLFPxWKuRpivZd_ivR2EvEzKrDUu&index=2
-- https://oeis.org/A003001

import System.Environment(getArgs)
import Data.List(intercalate)

main = do
    args <- getArgs
    let n = read (head args) :: Integer
        nMult = selfMult n
    putStrLn (intercalate "\n" (map show nMult))
    putStrLn (show n ++ " has a multiplicative persistence of " ++ (show $ length nMult - 1))

selfMult :: (Integral a) => a -> [a]
selfMult n
  | length ndigits < 2 = [n]
  | otherwise = n : (selfMult $ product ndigits)
  where ndigits = digits n

digits 0 = []
digits x = digits (x `div` 10) ++ [x `mod` 10]