A [Mersenne prime](https://en.wikipedia.org/wiki/Mersenne_prime) is a prime number that can be represented as:
Mn = 2^(n) - 1. Therefore, every Mersenne prime is one less than a power of two. 
Write a function that will return whether the given integer `n` will produce a Mersenne prime or not.
The tests will check random integers up to 2000.
def valid_mersenne(n):
    return n in {2,3,5,7,13,17,19,31,61,89,107,127,521,607,1279}
def valid_mersenne(n):
    return n in {2,3,5,7,13,17,19,31,61,89,107,127,521,607,1279}