The largest known prime number is equivalent to 2^(57,885,161) -1, and it is 17,425,170 digits long. It was discovered on Jan. 25, 2013 at the University of Central Missouri.
A prime number is a number that is greater than one and can only be divided by one and itself. The largest prime number is part of a special class of highly rare prime numbers referred to as Mersenne primes. Including 2^(57,885,161) -1, there are only 48 known Mersenne prime numbers to date. Mersenne primes are numbers that are one less than the power of two; Mersenne prime = 2^n -1.