PrimeGrid’sThe Riesel Problem
On 14 Jan 2011 9:03:07 UTC, PrimeGrid’s The Riesel Problem project eliminated
k=428639 by finding the Mega prime:
428639*2^3506452-1
The prime is 1,055,553 digits long and enters Chris Caldwell's “The Largest Known
Primes Database” (http://primes.utm.edu/primes) ranked 29th overall. This is the2nd largest prime found in The Riesel Problem and PrimeGrid's second eliminationin 2 months. 62 k's now remain.
The discovery was made by Brett Melvold of Australia using an Intel i7 920 @
2.67GHz with 6GB RAM, running Windows 7. This computer took 11 hours and 13
minutes to complete the primality test using LLR. Brett is a member of theBOINC@AUSTRALIA team.
The prime was verified on 18 Jan 2011 10:16:52, by Jason Sarley of the UnitedStates using an Intel Core2 Duo P8700 @ 2.53GHz with 4 GB RAM, running Darwin
10.6. This computer took a little over 8 hours 17 minutes to complete the primality
test using LLR. Jason is a member of the NullGrid team.
The credits for the discovery are as follows:
1. Brett Melvold (Australia), discoverer
2. PrimeGrid, et al.
3. Srsieve, sieving program developed by Geoff Reynolds
4. 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=97496
Hans Ivar Riesel, a Swedish mathematician, showed in 1956 that there are an
infinite number of positive odd integer k's such that k*2^n-1 is composite (notprime) for every integer n>=1. These numbers are now called Riesel numbers. He
further showed that k=509203 was such one.
It is conjectured that 509203 is the smallest Riesel number. The Riesel Problem
consists in determining that 509203 is the smallest Riesel number. To show that itis the smallest, a prime of the form k*2^n-1 must be found for each of the positive
integer k's less than 509203. For more information about The Riesel Problem,
please visit Wilfrid Keller's The Riesel Problem: Definition and Status(http://www.prothsearch.net/rieselprob.html).
Using a single PC would have taken years to find this prime. So this timely
discovery would not have been possible without the hundreds of volunteers who
contributed their spare CPU cycles. A special thanks to everyone who offered theiradvice and/or computing power to the search - especially Sean Faith and BrianCarpenter who provided support information from the previous Riesel Sieve effort.
The Riesel Problem project will continue to seek primes for the 62 remaining k's.
To join the search please visit PrimeGrid: http://www.primegrid.com

PrimeGrid’s
The Riesel Problem
About PrimeGrid
PrimeGrid is a distributed computing project, developed by Rytis Slatkevičius, whichutilizes BOINC and PRPNet to search for primes. PrimeGrid's primary goal is to bringthe excitement of prime finding to the "everyday" computer user. Simply download
the software and let your computer do the rest. Participants can choose from avariety of prime forms to search. With a little patience, you may find a large oreven record breaking prime.
BOINC
The Berkeley Open Infrastructure for Network Computing (BOINC) is asoftware platform for distributed computing using volunteered computerresources. It allows users to participate in multiple distributed computing
projects through a single program. Currently BOINC is being developed by ateam based at the University 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, 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