PrimeGrid’sSierpinski/Riesel Base 5 Problem
On 21 October 2015, 05:23:34 UTC, PrimeGrid’s Sierpinski/Riesel Base 5 Problem
project eliminated k=100186 by finding the mega prime:100186*52079747-1
The prime is 1,453,686 digits long and will enter Chris Caldwell's “The Largest Known
Primes Database” (http://primes.utm.edu/primes) ranked 53rd overall. This is thelargest known base 5 mega prime. 78 k's now remain in the Riesel Base 5 Problem.
The discovery was made by Toshitaka Kumagai of Japan using an Intel(R) Xeon(R)CPU E3-1220 V2 @ 3.10GHz with 32GB RAM running Linux. This computer tookabout 15 hours 41 minutes to complete the primality test using LLR.
The prime was verified on 21 October 2015, 18:46:14 UTC by Scott Brown of theUnited States using an Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz with 8GB RAM
running Microsoft Windows 7 Enterprise. This computer took about 27 hours 36
minutes to complete the primality test using LLR. Scott is a member of the Duke
University team.
Credits for the discovery are as follows:
1.
2.
3.
4.

Toshitaka Kumagai (Japan), discoverer
PrimeGrid, et al.
Srsieve, sieving program developed by Geoff Reynolds
LLR, primality program developed by Jean Penné

Entry in “The Largest Know Primes Database” can be found here:
http://primes.utm.edu/primes/page.php?id=120481

Using a single PC would have taken years to find this prime. So this timely discovery
would not have 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 thescenes to make a find like this possible.
The Sierpinski/Riesel Base 5 Problem will continue to search for more primes. To join
the search please visit PrimeGrid: http://www.primegrid.com

PrimeGrid’s
Sierpinski/Riesel Base 5 Problem
About PrimeGrid
PrimeGrid is a distributed computing project, developed by Rytis Slatkevičius, Lennart
Vogel, and John Blazek, which utilizes BOINC and PRPNet to search for primes.
PrimeGrid's primary goal is to bring the excitement of prime finding to the "everyday"
computer user. Simply download the software 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 to participate in multiple distributed computing projects through asingle program. Currently BOINC is being developed by a team based at theUniversity of California, Berkeley led by David 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
specifically designed 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