A prime number is a whole number greater than one that can only be divided by itself and one. The best known primes are the small ones such as 2, 3, 5, and 7. New, very large ones are difficult to find and of great interest to mathematicians.
The newest prime number, also known as M74207281, has 22,338,618 digits and is the number you get when you multiply 74,207,281 twos together and then subtract one, says the Great Internet Mersenne Prime Search, which announced the discovery.
You can download a zip file of the entire number here.
That makes it a special kind of number called a Mersenne prime. All Mersenne primes can be produced by multiplying together a certain number of twos and subtracting one. Only 49 Mersenne primes have ever been discovered, including the new one.