On 11 January 2016, 10:02:08 UTC, PrimeGrid’s Sierpinski/Riesel Base 5 Problem project eliminated k=306398 by finding the mega prime:
The prime is 1,476,517 digits long and enters Chris Caldwell's The Largest Known Primes Database ranked 50th overall. This is the largest known base 5 mega prime. 77 k's now remain in the Riesel Base 5 Problem.
The discovery was made by André Ahlfors Dahl (NocFlame) of Sweden using an Intel(R) Xeon(R) CPU W3520 @ 2.67GHz with 16GB RAM running Linux. This computer took about 77 hours 10 minutes to complete the primality test using LLR. André is a member of the Gridcoin team.
The prime was verified on 17 January 2016, 19:36:26 UTC by evaotaku00 of the United States using an Intel(R) Xeon(R) CPU X5355 @ 2.66GHz with 24GB RAM running Darwin. This computer took about 77 hours 10 minutes to complete the primality test using LLR. evaotaku00 is a member of the Ars Technica team.
For more details, please see the official announcement.