A FedEx employee in Tennessee has discovered the largest known prime number. At 23,249,425 digits long, the number is nearly a million digits longer than the previous record-holder.

The number in question was discovered using software from the Great Internet Mersenne Prime Search (GIMPS), a collaborative project used to search for Mersenne prime numbers. You may be familiar with one of the group’s pieces of software, Prime95, which for years has been used as a PC benchmarking application.

Jonathan Pace, a GIMPS volunteer for over 14 years, discovered the 50th known Mersenne prime on December 26, 2017. The number was calculated by multiplying the number two 77,232,917 times and then subtracting one. A Zip file of the number is available for download if you're curious.

It can be difficult to wrap one’s head around a number that’s more than 23 million digits long. According to Mersenne.org, the number is long enough to fill an entire shelf of books totaling 9,000 pages. Put another way, “If every second you were to write five digits to an inch then 54 days later you'd have a number stretching over 73 miles (118 km).” That’s almost three miles longer than the previous record prime.

Pace, a 51-year-old electrical engineer living in Germantown, Tennessee, runs Prime95 on PCs and servers that he oversees as a system administrator. The machine that discovered the new prime is powered by a quad-core Intel Core i5-6600 processor. It took the system six days to prove the number prime which has since been independently verified using four different programs on various hardware configurations.

Lead image via Robert Brook, Science Photo Library