Largest Prime Number Ever Identified—And It's 22 Million Digits Long

The new prime number, the largest yet "discovered," just keeps going and going. Great Internet Mersenne Prime Search

Say hello to the world's largest prime number.

Prime numbers, which are divisible only by one and themselves—such as one, two, three, five, seven, 11 and so on—become less common as numbers get larger.

A group a volunteers around the world have been searching for the largest ones, using computer software, in a project called the Great Internet Mersenne Prime Search (GIMPS). One such volunteer, mathematician Curtis Cooper at the University of Central Missouri, has found the biggest one to date: 274,207,281 − 1, according to the group. This enormous number is 22,338,618 digits long, and is 5 million digits longer than the previous record holder.

The number is so large that if it were put on paper in extremely fine print (with characters one millimeter in width), it would stretch out for nearly 14 miles, explains mathematician Matt Parker in the above video.

Why search for such numbers? Primes are important in cryptography because they can serve as "keys," akin to passwords, that are difficult to decrypt. The new number, however, "is too large to currently be of practical value," according to GIMPS. At this point, the search is more about testing the limits of computing power, and is, for volunteers, an enjoyable pastime, equivalent to exploring the unknown extremes of the numerical universe.

If you're so inclined, you can download a .zip file of the number here. (Maybe search for your social security number! Go nuts!)