Not the Prius Prime, but another Prime... "There’s a new largest known prime number in town, with a whopping 23,249,425 digits. The figure is calculated by multiplying 2 by itself 77,232,917 times and then subtracting 1. Announced on Jan. 3, the number is almost a million digits longer than the last record-breaking prime." The largest known prime number was just discovered - The Washington Post
These are Mersenne primes that all take the form (2^n)-1. They can be calculated relatively simply by some math I don't know. There are certainly many other much smaller primes that have not yet been found because the math in general is way too hard.
