Now we have more than 23 million but in the 1950s, the largest known prime number had 44 digits

To a small but dedicated group of people, one question dominates their lives—when will we discover a one-billion digit prime?

A prime number is only divisible by one or itself (think 3, 5, 7, 11). Jonathan Pace had been searching for the largest prime for more than a decade until, at the end of last year, software on a computer the electrical engineer installed at his church in Tennessee unearthed a record-breaking 23,249,425-digit prime.

That number is 2^77,232,917-1.

Before the information age, some of the world's smartest mathematicians could only prove that (2¹⁴⁸+1)/17, a measly 44-digit number, was prime.

YearLargest primeDigitsProver15882^17-16Cataldi15882^19-16Cataldi17722^31-110Euler1867(2^59-1)/17995113Landry18762^127-139Lucas1951(2^148+1)/1744Ferrier

Then came computers, and the length of the largest known prime grew rapidly. However, we're still a ways from a billion.