There's a giant prime number with 24,862,048 digits - Apparently.
The largest known prime number as of 2018 is a Mersenne prime, a prime that can be written in the form 2^p - 1 where p is also prime. This particular prime number, 2^82,589,933 - 1, was discovered by a distributed computing project called the Great Internet Mersenne Prime Search (GIMPS). The number is so large that it would take a standard computer over 5 million years to calculate its square root.