On 30 May 2016, 18:15:42 UTC, PrimeGrid’s Sierpinski/Riesel Base 5 Problem project eliminated k=53546 by finding the mega prime:
The prime is 1,549,387 digits long and enters Chris Caldwell's The Largest Known Primes Database ranked 48th overall. This is the largest known base 5 mega prime. 75 k's now remain in the Riesel Base 5 Problem.
The discovery was made by Tom Greer (tng*) of the United States using an Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz with 32GB RAM running Microsoft Windows 7 Professional. This computer took about 29 hours 24 minutes to complete the primality test using LLR. Tom is a member of the Sicituradastra. team.
The prime was verified on 2 June 2016, 01:20:10 UTC by John Parker (Mike Parker) of the United States using an Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz with 16GB RAM running Microsoft Windows 10. This computer took about 80 hours 8 minutes to complete the primality test using LLR. John is a member of the SETI.USA team.
For more details, please see the official announcement.