On 11 March 2018, 23:54:40 UTC, PrimeGrid’s Generalized Cullen/Woodall Prime Search found the largest known Generalized Cullen prime:
Generalized Cullen numbers are of the form: n*b^n+1. Generalized Cullen numbers that are prime are called Generalized Cullen primes. For more information, please see “Cullen prime” in The Prime Glossary.
The prime is 2,913,785 digits long and enters Chris Caldwell's The Largest Known Primes Database ranked 1st for Generalized Cullen primes and 27th overall.
Base 41 was one of 12 prime-less Generalized Cullen bases below b=121 that PrimeGrid is searching. The remaining bases are 13, 25, 29, 47, 49, 55, 69, 73, 101, 109 & 121.
The discovery was made by Hiroyuki Okazaki (zunewantan) of Japan using an Intel(R) Xeon(R) E5-2670 CPU @ 2.60GHz with 4GB RAM, running Linux. This computer took about 7 hours and 13 minutes to complete the primality test using multithreaded LLR. Hiroyuki is a member of the Aggie The Pew team.
The prime was verified on 12 March 2018 09:07:23 UTC by Scott Brown (Scott Brown) of the United States using an Intel(R) CPU @ 2.30GHz with 16GB RAM, running Windows 10 Professional Edition. This computer took about 15 hours 22 minutes to complete the primality test using LLR. Scott is also a member of the Aggie The Pew team.
For more details, please see the official announcement.