PrimeGrid’s
Generalized Cullen/Woodall Prime Search
On 18 January 2018, 19:39:18 UTC, PrimeGrid’s Generalized Cullen/Woodall Prime Searchfound the largest known Generalized Cullen prime:1323365*116

1323365+1

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 (http://primes.utm.edu/glossary/xpage/Cullens.html).

The prime is 2,732,038 digits long and enters Chris Caldwell's “The Largest Known Primes
stthDatabase” (http://primes.utm.edu/primes) ranked 1 for Generalized Cullen primes and 30overall.
Base 116 was one of 13 prime-less Generalized Cullen bases below b=121 that PrimeGrid issearching. The remaining bases are 13, 25, 29, 41, 47, 49, 55, 69, 73, 101, 109 & 121.
The discovery was made by Scott Brown of the United States using an Intel(R) Core(TM) i74770S CPU @ 3.10GHz with 4GB RAM, running Windows 10 Enterprise Edition. This computer
took about 8 hours and 34 minutes to complete the primality test using multithreaded LLR. Scottis a member of the Aggie The Pew team.
The prime was verified on 19 January 2018 17:24:17 UTC by Serge De Saffel of Belgium using
an Intel(R) Core(TM) i5-6600K CPU @ 3.50GHz with 16GB RAM, running Windows 10 Education
Edition. This computer took about 15 hours 22 minutes to complete the primality test using LLR.
Serge is a member of the team Sicituradastra.
The credits for the discovery are as follows:
1.
2.
3.
4.
5.

Scott Brown (United States), discoverer
PrimeGrid, et al.
MultiSieve, sieve program developed by Mark Rodenkirch
gcwsieve, sieve program developed by Geoff Reynolds
LLR, primality program developed by Jean Penné

Entry in “The Largest Known Primes Database” can be found here:
http://primes.utm.edu/primes/page.php?id=124153
Using a single PC would have taken years to find this prime. So this timely discovery would nothave been possible without the thousands of volunteers who contributed their spare CPU cycles.
A special thanks to everyone who contributed their advice and/or computing power to the search especially all the sievers who work behind the scenes to make a find like this possible.
PrimeGrid’s Generalized Cullen/Woodall Prime Search will continue seeking primes for otherprimeless bases. To join the search please visit PrimeGrid: http://www.primegrid.com

PrimeGrid’sGeneralized Cullen/Woodall Prime Search
About PrimeGrid
PrimeGrid is a distributed computing project, developed by Rytis Slatkevičius and currently
administered by Iain Bethune, James Breslin, Scott Brown, Ulrich Fries, Michael Goetz, Roger
Karpin, Rytis Slatkevičius, and Van Zimmerman.
PrimeGrid utilizes BOINC and PRPNet to search for primes with the primary goal of bringing theexcitement of prime finding to the "everyday" computer user. Simply download the software andlet your computer do the rest. Participants can choose from a variety of prime forms to search.
With a little patience, you may find a large or even record breaking prime.
BOINC
The Berkeley Open Infrastructure for Network Computing (BOINC) is a software platform
for distributed computing using volunteered computer resources. It allows users toparticipate in multiple distributed computing projects through a single program. Currently
BOINC is being developed by a team based at the University of California, Berkeley led byDavid Anderson.
This platform currently supports projects from biology to math to astronomy. For moreinformation, please visit BOINC: http://boinc.berkeley.edu
PRPNetPRPNet is a client/server application written by Mark Rodenkirch that is specificallydesigned to help find prime numbers of various forms. It is easily ported between various
OS/hardware combinations. PRPNet does not run each PRP test itself, but relies on helper
programs, such as LLR, PFGW, phrot, wwww, and genefer to do the work.
For more information, please visit PrimeGrid’s PRPNet forum thread:
http://www.primegrid.com/forum_thread.php?id=1215
For more information about PrimeGrid and a complete list of available prime search projects,
please visit: http://www.primegrid.com