PrimeGrid’s
Proth Prime Search	  On 9 Sep 2011 11:50:50 UTC, PrimeGrid's Proth Prime Search project found a prime Fermat
divisor:25*22141884+1 Divides F(2141872)

The prime is 644,773 digits long and will enter Chris Caldwell's "The Largest Known Primes
ththDatabase" (http://primes.utm.edu/primes) ranked 5 for prime Fermat divisors and 88 overall. Itthndis the 9 divisor found in 2011 and 292 overall.
The discovery was made by Grzegorz Granowski of Poland using an Intel Xeon X5550 @
2.67GHz with 12 GB RAM running Windows Vista x64. This computer took just over 58 minutes
and 28 seconds to complete the primality test using LLR. Grzegorz is a member of the Polish
National Team.
The prime was verified on 11 Sep 2011 12:02:18 UTC, by John R. H. Graham of Canada using
an Intel i7 920 @ 2.67GHz with 12 GB RAM running Windows 7 x64. This computer took about 1
hour and 47 minutes to complete the primality test using LLR. John is a member of Team
Canada.
The credits for the discovery are as follows:
1.
2.
3.
4.
5.
6.

Grzegorz Granowski (Poland), discoverer
PrimeGrid, et al.
Srsieve, sieving program developed by Geoff Reynolds
PSieve, sieving program developed by Ken Brazier and Geoff Reynolds
LLR, primality program developed by Jean Penné
OpenPFGW, a primality program developed by Chris Nash & Jim Fougeron withmaintenance and improvements by Mark Rodenkirch

Entry in "The Largest Know Primes Database" can be found here:
http://primes.utm.edu/primes/page.php?id=101943.
Fermat number divisibility (including generalized and extended) was checked by OpenPFGW
using the following settings: -gxo –a2 25*2^2141884+1. For more information about Fermat andgeneralized Fermat number divisors, please see Wilfrid Keller's sites:••

http://www.prothsearch.net/fermat.html
http://www1.uni-hamburg.de/RRZ/W.Keller/GFNfacs.html

Generalized and extended generalized Fermat number divisors discovered are as follows:
25*2^2141884+1 Divides GF(2141871,5)
25*2^2141884+1 Divides xGF(2141872,5,2)
25*2^2141884+1 Divides xGF(2141867,5,4)

25*2^2141884+1 Divides xGF(2141872,8,5)
25*2^2141884+1 Divides GF(2141872,10)

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.
This is PrimeGrid’s 8th prime Fermat divisor. The Proth Prime Search will continue to search formore primes. To join the search please visit PrimeGrid: http://www.primegrid.com

PrimeGrid’sProth Prime Search	  About PrimeGrid

PrimeGrid is a distributed computing project, developed by Rytis Slatkevičius, Lennart Vogel, andJohn Blazek, which utilizes BOINC and PRPNet to search for primes. PrimeGrid's primary goal isto bring the excitement of prime finding to the "everyday" computer user. Simply download thesoftware and let 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 more
information, please visit BOINC: http://boinc.berkeley.edu
PRPNet
PRPNet 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 variousOS/hardware combinations. PRPNet does not run each PRP test itself, but relies on helper
programs, such as LLR, PFGW, phrot, 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