Welcome to the Hans Ivar Riesel's 90th Birthday Challenge
The third Challenge of the 2019 Challenge series is a 7 day challenge to celebrate Hans Ivar Riesel's 90th Birthday! The challenge is being offered on the The Riesel Problem (TRP) (LLR) application.
Hans Ivar Riesel (May 28, 1929 in Stockholm – December 21, 2014) was a Swedish mathematician who discovered the 18th known Mersenne prime in 1957, using the computer BESK (Binär Elektronisk SekvensKalkylator, Swedish for "Binary Electronic Sequence Calculator"), this prime is 2^32171 and consists of 969 digits. He held the record for the largest known prime from 1957 to 1961, when Alexander Hurwitz discovered a larger one. Riesel also discovered the Riesel numbers as well as developed the Lucas–Lehmer–Riesel test. After having worked at the Swedish Board for Computing Machinery, he was awarded his Ph.D. from Stockholm University in 1969 for his thesis Contributions to numerical number theory, and in the same year joined the Royal Institute of Technology as a senior lecturer and associate professor.
To participate in the Challenge, please select only the The Riesel Problem LLR (TRP) project in your PrimeGrid preferences section. The challenge will begin 24th May 2019 00:00 UTC and end at 31st May 2019 00:00 UTC.
Application builds are available for Linux 32 and 64 bit, Windows 32 and 64 bit and MacIntel. Intel CPUs with AVX capabilities (Sandy Bridge, Ivy Bridge, Haswell, Broadwell, Skylake, Kaby Lake, Coffee Lake) will have a very large advantage, and Intel CPUs with FMA3 (Haswell, Broadwell, Skylake, Kaby Lake, Coffee Lake) will be the fastest.
The latest version of LLR now supports AVX512, which is significantly faster on CPUs that support it. Requires anonymous platform mechanism. For more info see the thread, LLR 3.8.23 released.
ATTENTION: The primality program LLR is CPU intensive; so, it is vital to have a stable system with good cooling. It does not tolerate "even the slightest of errors." Please see this post for more details on how you can "stress test" your computer. Tasks on one CPU core will take 12 hours on fast/newer computers and 1.5+ days on slower/older computers. If your computer is highly overclocked, please consider "stress testing" it. Sieving is an excellent alternative for computers that are not able to LLR. :)
Highly overclocked Haswell, Broadwell, Skylake, Kaby Lake or Coffee Lake (i.e., Intel Core i7, i5, and i3 4xxx or better) computers running the application will see fastest times. Note that TRP is running the latest FMA3 version of LLR which takes full advantage of the features of these newer CPUs. It's faster than the previous LLR app and draws more power and produces more heat. If you have a Haswell, Broadwell, Skylake, Kaby Lake or Coffee Lake CPU, especially if it's overclocked or has overclocked memory, and haven't run the new FMA3 LLR before, we strongly suggest running it before the challenge while you are monitoring the temperatures.
Please, please, please make sure your machines are up to the task.
Multithreading optimisation instructions
Those looking to maximise their computer's performance during this challenge, or when running LLR in general, may find this information useful.
 Your mileage may vary. Before the challenge starts, take some time and experiment and see what works best on your computer.
 If you have an Intel CPU with hyperthreading, either turn off the hyperthreading in the BIOS, or set BOINC to use 50% of the processors.
 If you're using a GPU for other tasks, it may be beneficial to leave hyperthreading on in the BIOS and instead tell BOINC to use 50% of the CPU's. This will allow one of the hyperthreads to service the GPU.
 Use LLR's multithreaded mode. It requires a little bit of setup, but it's worth the effort. Follow these steps:
Time zone converter:
The World Clock  Time Zone Converter
NOTE: The countdown clock on the front page uses the host computer time. Therefore, if your computer time is off, so will the countdown clock. For precise timing, use the UTC Time in the data section at the very top, above the countdown clock.
Scoring Information
Scores will be kept for individuals and teams. Only tasks issued AFTER 24th May 2019 00:00 UTC and received BEFORE 31st May 2019 00:00 UTC will be considered for credit. We will be using the same scoring method as we currently use for BOINC credits. A quorum of 2 is NOT needed to award Challenge score  i.e. no double checker. Therefore, each returned result will earn a Challenge score. Please note that if the result is eventually declared invalid, the score will be removed.
At the Conclusion of the Challenge
We kindly ask users "moving on" to ABORT their tasks instead of DETACHING, RESETTING, or PAUSING.
ABORTING tasks allows them to be recycled immediately; thus a much faster "clean up" to the end of an LLR Challenge. DETACHING, RESETTING, and PAUSING tasks causes them to remain in limbo until they EXPIRE. Therefore, we must wait until tasks expire to send them out to be completed.
Please consider either completing what's in the queue or ABORTING them. Thank you. :)
About the Riesel Problem
In 1956, Hans Riesel showed that there are an infinite number of positive odd integer k's such that k*2^n1 is composite (not prime) 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 of determining that 509203 is the smallest Riesel number. To show that it is the smallest, a prime of the form k*2^n1 must be found for each of the positive integer k's less than 509203. As of December 13th, 2017, there remain 49 k's for which no primes have been found. They are as follows:
2293, 9221, 23669, 31859, 38473, 46663, 67117, 74699, 81041, 93839, 97139, 107347, 121889, 129007, 143047, 146561, 161669, 192971, 206039, 206231, 215443, 226153, 234343, 245561, 250027, 315929, 319511, 324011, 325123, 327671, 336839, 342847, 344759, 362609, 363343, 364903, 365159, 368411, 371893, 384539, 386801, 397027, 409753, 444637, 470173, 474491, 477583, 485557, 494743
For a more detailed history and status of the Riesel problem, please visit Wilfrid Keller's The Riesel Problem: Definition and Status.
The Riesel problem is to k*2^n1 as the Sierpinski problem is to k*2^n+1. There is no equivalent to the 'prime' Sierpinski problem since k=509203, the conjectured smallest Riesel number, is prime.
Last Primes found at PrimeGrid
402539*2^71730241 by Walter Darimont on 2 October 2014. Official Announcement.
502573*2^71819871 by Denis Iakovlev on 4 October 2014. Official Announcement.
273809*2^89324161 by Wolfgang Schwieger on 13 December 2017. Official Announcement.
What is LLR?
The LucasLehmerRiesel (LLR) test is a primality test for numbers of the form N = k*2^n − 1, with 2^n > k. Also, LLR is a program developed by Jean Penne that can run the LLRtests. It includes the Proth test to perform +1 tests and PRP to test non base 2 numbers. See also:
(Edouard Lucas: 18421891, Derrick H. Lehmer: 19051991, Hans Riesel: 19292014).
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