17 lines
516 B
Haskell
17 lines
516 B
Haskell
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import Data.List (find, group)
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isqrt :: (Integral n) => n -> n
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isqrt = floor . sqrt . fromIntegral
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primeFactors :: (Integral n) => n -> [n]
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primeFactors n =
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case find ((== 0) . (n `mod`)) [2 .. isqrt n] of
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Nothing -> [n]
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Just m -> m : primeFactors (n `div` m)
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primeFactorsMult :: (Integral n) => n -> [(n, n)]
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primeFactorsMult = map (\g -> (head g, fromIntegral $ length g)) . group . primeFactors
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phi :: (Integral n) => n -> n
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phi = product . map (\(p, r) -> (p - 1) * p ^ (r - 1)) . primeFactorsMult
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