M51 normally refers to the 51th Mersenne prime, in order of size from the smallest to greatest. This is the primary usage and what is referred to in the rest of this article.
The official discovery date for prime 282,589,933-1 was 2018-12-21 and has 24,862,048 digits.
A computer volunteered by Patrick Laroche made the find on 2018-12-07. The primality proof took twelve days of non-stop computing on a machine with an Intel i5-4590T CPU.
The volunteers that ran these tests were:
- Andreas Höglund verified the prime using CUDALucas running on a NVidia V100 GPU in 21 hours.
- Andreas Höglund also verified the prime using Mlucas running on 16 cores of an Amazon AWS instance in 72 hours.
- Aaron Blosser also verified it using Prime95 on an Intel 7700K processor in 6 days, 8 hours.