Created
August 4, 2013 20:40
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Prime numbers
Simple recursion to find primality up to 40,000
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| defmodule Prime do | |
| def known_primes, do: [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199] | |
| def is_prime(n) when n > 9409, do: :cannot_calculate | |
| def is_prime(n) when n < 2, do: false | |
| def is_prime(2), do: true | |
| def is_prime(n), do: check_primes(n, known_primes) | |
| def check_primes(_,[]), do: true | |
| def check_primes(n, [head|_tail]) when head*head > n, do: true | |
| def check_primes(n, [head|tail]), do: rem(n, head) != 0 and check_primes(n, tail) | |
| end |
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