The largest prime number ever found has been confirmed – it’s 2 multiplied by itself 74,107,18 times, minus one (in other words, it’s a Mersenne Prime) and it has 22,338,618 digits. It was discovered as part of the Great Internet Mersenne Prime Search or GIMPS, an early citizen-science project in which people allow their computers to do calculations on their free time. GIMPS has been around 20 years, which is a lot in Internet time. From the report (read the whole thing here):
The primality proof took 31 days of non-stop computing on a PC with an Intel I7-4790 CPU. To prove there were no errors in the prime discovery process, the new prime was independently verified using both different software and hardware.
49 Mersenne Primes are known, 14 of which have been found by GIMPS.