7 lines
195 B
Haskell
7 lines
195 B
Haskell
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import Math.NumberTheory.Primes.Factorisation
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totient :: Integer -> Integer
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totient n = foldr (\(p, _) acc -> acc * (p-1) `div` p) n $ factorise n
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main = print $ sum $ map totient [2..1000000]
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