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26 lines
717 B
Haskell
26 lines
717 B
Haskell
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{- Find the 10001st prime.
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By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
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What is the 10001st prime number?
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-}
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import Text.Printf
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is_prime :: (Integral a) => a -> Bool
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is_prime n
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| n == 1 = False
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| n < 4 = True
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| n `rem` 2 == 0 = False
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| n < 9 = True
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| n `rem` 3 == 0 = False
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| otherwise = do
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let f = sqrt (fromIntegral n)
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let checkprime x = (n `rem` x == 0 || n `rem` (x + 2) == 0)
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not (or (map checkprime (takeWhile (<= floor f) [5,11..])))
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primes = filter is_prime (2:[3,5..])
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main = do
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printf " 6th prime: %d\n" (primes !! 5 :: Integer)
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printf "10001th prime: %d\n" (primes !! 10000 :: Integer)
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