content: --------------------------------------------------------------------------------
  -- MIT License
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  -- Copyright (C) 2023--2024 Duck McSouls <quacksouls [AT] gmail [DOT] com>
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  --------------------------------------------------------------------------------
  
  import Text.Printf
  
  -- | Remove multiples of a specific integer due to fear of the number.
  notN :: Integer -> [Integer] -> [Integer]
  notN n xs = filter (\x -> mod x n /= 0) xs
  
  -- | Remove multiples of the following numbers: 4, 9, 13, 17, 39, 666.
  main = do
      let num = [1 .. 1000]
      let ell = notN 666 $ notN 39 $ notN 17 $ notN 13 $ notN 9 $ notN 4 num
      let n = length ell
      printf "How many numbers between 1 and 1,000 that do not induce fear: %d\n" n
      -- Same as above, but use list comprehension.
      let ellc =
              [ x
              | x <- num
              , mod x 4 /= 0
              , mod x 9 /= 0
              , mod x 13 /= 0
              , mod x 17 /= 0
              , mod x 39 /= 0
              , mod x 666 /= 0
              ]
      putStrLn "\nUsing list comprehension"
      printf "How many non-fear inducing numbers: %d\n" $ length ellc
  