Remark

Although it is known that there are infinitely many prime numbers, we actually only know a finite number of them. At present (June, 1998) the largest known prime number is

23021377 - 1.

This prime number was found by a 19 year old student, Roland Clarkson, January, 1998. Clarkson was one of more than 4000 people joining a large project on the internet to search for so-called Mersenne primes. These are primes of the form

2n - 1.

The prime number 23021377 - 1 consists of 909526 digits!

Prime numbers of the form 2n - 1 are called Mersenne primes, since they were studied first by Marin Mersenne (1588-1648). It is easy to prove that a number 2n - 1 can be prime only when n itself is a prime. Examples of Mersenne primes are 3 = 22 - 1, 7 = 23 - 1, 31 = 25 - 1, 127 = 27 - 1. Mersenne found 211 - 1 not to be prime. Can you find the prime divisors?
Marin Mersenne