On 2 September 2019, 03:39:59 UTC, PrimeGrid’s Generalized Cullen/Woodall Prime Search found the largest known Generalized Cullen prime:
Generalized Cullen numbers are of the form: n*bn+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 3,921,539 digits long and enters Chris Caldwell's The Largest Known Primes Database ranked 1st for Generalized Cullen primes and 21st overall.
Base 25 was one of 11 primeless Generalized Cullen bases for b ≤121 that PrimeGrid is searching. The remaining bases are 13, 29, 47, 49, 55, 69, 73, 101, 109 & 121.
The discovery was made by Tom Greer (tng*) of the United States using an Intel(R) Core(TM) i9-9900X CPU @ 3.50GHz with 32GB RAM, running Microsoft Windows 10 Professional x64 Edition. His computer took 3 hours and 23 minutes to complete the primality test using multithreaded LLR. Tom is a member of the Sicituradastra team.
The prime was verified on 3 September 2019 05:15:11 UTC by Tim Terry (TimT) of the United States using an Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz with 16GB RAM, running Microsoft Windows 10 Professional x64 Edition. This computer took about 24 hours 11 minutes to complete the primality test using multithreaded LLR. Tim is a member of the Aggie The Pew team.
For more details, please see the official announcement.