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cacharle/prime.hs

Created September 4, 2019 18:19
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prime.hs
isPrime :: Int -> Bool
isPrime 2 = True
isPrime 3 = True
isPrime x
| x < 2 = False
| x `mod` 2 == 0 || x `mod` 3 == 0 = False
| otherwise = divCheck 5
where divCheck d
| d * d > x = True
| x `mod` d == 0 || x `mod` (d + 2) == 0 = False
| otherwise = divCheck (d + 6)
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