diff --git a/maths/lucas_lehmer_primality_test.py b/maths/lucas_lehmer_primality_test.py new file mode 100644 index 000000000000..44e41ba58d93 --- /dev/null +++ b/maths/lucas_lehmer_primality_test.py @@ -0,0 +1,42 @@ +# -*- coding: utf-8 -*- +""" + In mathematics, the Lucas–Lehmer test (LLT) is a primality test for Mersenne numbers. + https://en.wikipedia.org/wiki/Lucas%E2%80%93Lehmer_primality_test + + A Mersenne number is a number that is one less than a power of two. + That is M_p = 2^p - 1 + https://en.wikipedia.org/wiki/Mersenne_prime + + The Lucas–Lehmer test is the primality test used by the + Great Internet Mersenne Prime Search (GIMPS) to locate large primes. +""" + + +# Primality test 2^p - 1 +# Return true if 2^p - 1 is prime +def lucas_lehmer_test(p: int) -> bool: + """ + >>> lucas_lehmer_test(p=7) + True + + >>> lucas_lehmer_test(p=11) + False + + # M_11 = 2^11 - 1 = 2047 = 23 * 89 + """ + + if p < 2: + raise ValueError("p should not be less than 2!") + elif p == 2: + return True + + s = 4 + M = (1 << p) - 1 + for i in range(p - 2): + s = ((s * s) - 2) % M + return s == 0 + + +if __name__ == "__main__": + print(lucas_lehmer_test(7)) + print(lucas_lehmer_test(11))