Welcome to the Good Riddance 2020! Challenge

The first challenge of the 2021 Series will be a 5-day challenge celebrating the end of the abomination which was the year 2020. The challenge will be offered on the PPS-DIV (LLR) application, beginning 14 January 00:00 UTC and ending 18 January 23:59 UTC.

To participate in the Challenge, please select only the Fermat Divisor Search LLR (PPS-DIV) project in your PrimeGrid preferences section.

Note on LLR2 tasks: LLR2 has eliminated the need for a full doublecheck task on each workunit, but has replaced it with a short verification task. Expect to receive a few tasks about 1% of normal length.

Application builds are available for Linux 32 and 64 bit, Windows 32 and 64 bit and MacIntel. Intel and recent AMD CPUs with FMA3 capabilities (Haswell or better for Intel, Zen-2 or better for AMD) will have a very large advantage, and Intel CPUs with dual AVX-512 (certain recent Intel Skylake-X and Xeon CPUs) will be the fastest.

Note that LLR is running the latest AVX-512 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, especially if they're highly overclocked. If you have certain recent Intel Skylake-X and Xeon CPUs, especially if it's overclocked or has overclocked memory, and haven't run the new AVX-512 LLR before, we strongly suggest running it before the challenge while you are monitoring the temperatures.

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 about 5 hours on fast/newer computers and 12 hours+ 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. :)

TL;DR: Please, please, please make sure your machines are up to the task.

Multi-threading is supported and IS recommended.

Those looking to maximize 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 a CPU with hyperthreading or SMT, either turn off this feature 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.

  
  

• The new multi-threading system is now live. Click here to set the maximum number of threads. This will allow you to select multi-threading from the project preferences web page. No more app_config.xml. It works like this:
  
  
  • In the preferences selection, there are selections for "max jobs" and "max cpus", similar to the settings in app_config.
    
  • Unlike app_config, these two settings apply to ALL apps. You can't chose 1 thread for SGS and 4 for SoB. When you change apps, you need to change your multithreading settings if you want to run a different number of threads.
    
  • There will be individual settings for each venue (location).
    
  • This will eliminate the problem of BOINC downloading 1 task for every core.
    
  • The hyperthreading control isn't possible at this time.
    
  • The "max cpus" control will only apply to LLR apps. The "max jobs" control applies to all apps.

  
  

• If you want to continue to use app_config.xml for LLR tasks, you need to change it if you want it to work. Please see this message for more information.
  
• Some people have observed that when using multithreaded LLR, hyperthreading is actually beneficial. We encourage you to experiment and see what works best for you.

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 14th January 2021 00:00 UTC and received BEFORE 19th January 2021 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 Fermat Divisor Search

In mathematics a Fermat number, named after Pierre de Fermat who first studied them, is a positive integer of the form F_n = 2²ⁿ+1, where n is a nonnegative integer.
The first few Fermat numbers are 3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, … (sequence A000215 in the OEIS).

Only five Fermat primes are known, and the Fermat numbers grow so quickly that it may be years before the first undecided case: F₃₃ = 2²³³+1 is shown prime or composite - unless we luck onto a divisor. Ever since Euler found the first Fermat divisor (divisor of a Fermat composite), factorers have been collecting these rare numbers.

Euler showed that every divisor of F_n (n greater than 2) must have the form k*2ⁿ⁺²+1 for some integer k. For this reason, when we find a large prime of the form k*2ⁿ+1 (with k small), we usually check to see if it divides a Fermat number. The probability of the number k*2ⁿ+1 dividing any Fermat number appears to be 1/k.

Any prime Generalised Fermat Number F_b,n = b²ⁿ+1 (with b an integer greater than one) is called a generalised Fermat prime (because they are Fermat primes in the special case b=2), Ribenboim (1996).
Riesel (1994) further generalised by defining Extended Generalised Fermat Numbers xGF_n,a,b = a²ⁿ+b²ⁿ.

In the Fermat Divisor Search we focus on special k's that are either small (generally gives high chance of dividing a Fermat number) or have special properties that makes them attractive.
First we searched k=19683 up to n=4M, (now complete).
Then we searched five additional k's, 1323 (even n only), 2187 (even n only), 3125, 3267 (even n only) and 3375, up to n=3.322M, (now complete).
Finally, we're currently searching 5<=k<=49 up to n=9M.

See also:

• The Top Twenty Fermat Divisors (The Prime Pages)
  
• The Top Twenty Generalized Fermat Divisors (bases 3,5,6,10,12) (The Prime Pages)
  
• Currently known Fermat divisors, sorted by k
  

What is LLR?

The Lucas-Lehmer-Riesel (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 LLR-tests. It includes the Proth test to perform +1 tests and PRP to test non base 2 numbers. See also:

• Lucas-Lehmer-Riesel test (WIKI)
  
• Download LLR by Jean Penné
  

What is LLR2?

LLR2 is an improvement to the LLR application developed by our very own Pavel Atnashev and stream. It utilizes Gerbicz checks to enable the Fast DoubleCheck feature, which will nearly double the speed of PrimeGrid's progress on the projects it's applied to. For more information, see this forum post.
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Time flies like an arrow. Fruit flies like a banana.

I'm looking forward to a new challenge season! I have a new cruncher on the way, this week, to retire a now useless (thanks to practical CPU sieving ending) pair of X5675s and easily outpace the both of them with a single "new" 5960X-and eventually a 22-core E5 2699 v4 :D. Hope it arrives in time to compete!

So I can set my threading optimally(ish), what are the current DIV FFT sizes?

Happy hunting, everybody!
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Eating more cheese on Thursdays.

Shiny new hardware is always nice to have :)

Current PPS-DIV FFT size is 480K

Shiny new hardware is always nice to have :)

Current PPS-DIV FFT size is 480K

Well, I've learned one important lesson from this challenge:

You can't run PG on an overclocked (350W!) 10980XE, 3930k, E3v3 Xeon, their respective high powered GPUs, and a laptop, plus pfsense router, storage server, all the networking gear for the house, 4 stereos (for surround sound!), and the bedrooms' lights off of one 20A, 120V circuit. (No, they were not all in one room.)

Oops.

I have a very old house where the wiring was updated to good, modern stuff in the 90s, but not, apparently, to the (then) standard of one circuit breaker per room.

The straw that broke the camel's back? I turned on the little monitor I use for direct access to the server.

There has been a relocation of hardware. >.<
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Eating more cheese on Thursdays.

Yawn...... these challenges have just descended into who can hire the most pc's to crunch with. I don't even bother looking at the ranks any more.

Crunching is already a very passive activity because the computers do the main job. Without assembling and looking after the hardware, and dealing with the heat and noise in my room, I would not feel like I did anything substantial to earn the credit. So, while others may see things differently, I definitely won't go for the cloud. Since I also enjoy crunching between the challenges, physical hardware is more cost-effective anyways, even accounting for the rather high electricity prices in my country. :)

I have been participating in every single challenge here since March 2008, and don't plan to change that. For me, the main challenge is to get the most out of my hardware, and if I manage to do that, I don't care whether I end up in 5th, 50th, or 500th place. There always have been participants with access to huge company or institute resources that I never had any chance to compete with. But I still look at the stats to applaud the huge home farms (there are still quite a few of them up there) and enjoy trying to catch other home users close to me (watch your back, Chooka :)).
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Challenge updates so far:

Challenge: Good Riddance 2020!
App: 32 (PPS-DIV)
Fast DC tasks are NOT included.
(As of 2021-01-17 01:30:47 UTC)

192099 tasks have been sent out. [CPU/GPU/anonymous_platform: 192099 (100%) / 0 (0%) / 0 (0%)]

Of those tasks that have been sent out:

8901 (5%) were aborted. [8901 (5%) / 0 (0%) / 0 (0%)]
819 (0%) came back with some kind of an error. [819 (0%) / 0 (0%) / 0 (0%)]
142297 (74%) have returned a successful result. [142300 (74%) / 0 (0%) / 0 (0%)]
40100 (21%) are still in progress. [40105 (21%) / 0 (0%) / 0 (0%)]

Of the tasks that have been returned successfully:

8740 (6%) are pending validation. [8742 (6%) / 0 (0%) / 0 (0%)]
133557 (94%) have been successfully validated. [133558 (94%) / 0 (0%) / 0 (0%)]
2 (0%) were invalid. [2 (0%) / 0 (0%) / 0 (0%)]
0 (0%) are inconclusive. [0 (0%) / 0 (0%) / 0 (0%)]

The current leading edge (i.e., latest work unit for which work has actually been sent out to a host) is n=8185926. The leading edge was at n=7870559 at the beginning of the challenge. Since the challenge started, the leading edge has advanced 4.01% as much as it had prior to the challenge!
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Time flies like an arrow. Fruit flies like a banana.

This is my first ever time in a challenge to get within no300! In August 2019 I was no302.....

Thank you to all the admins for organizing the challenge!!!
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My lucky number is 6219*2^3374198+1

Thanks to all who participated in the challenge! Here are the ending stats:

App: 32 (PPS-DIV)
Fast DC tasks are NOT included.
(As of 2021-01-19 19:26:00 UTC)

327007 tasks have been sent out. [CPU/GPU/anonymous_platform: 327007 (100%) / 0 (0%) / 0 (0%)]

Of those tasks that have been sent out:

30546 (9%) were aborted. [30546 (9%) / 0 (0%) / 0 (0%)]
4474 (1%) came back with some kind of an error. [4474 (1%) / 0 (0%) / 0 (0%)]
263315 (81%) have returned a successful result. [263315 (81%) / 0 (0%) / 0 (0%)]
15820 (5%) are still in progress. [15819 (5%) / 0 (0%) / 0 (0%)]

Of the tasks that have been returned successfully:

2942 (1%) are pending validation. [2942 (1%) / 0 (0%) / 0 (0%)]
260373 (99%) have been successfully validated. [260373 (99%) / 0 (0%) / 0 (0%)]
6 (0%) were invalid. [6 (0%) / 0 (0%) / 0 (0%)]
0 (0%) are inconclusive. [0 (0%) / 0 (0%) / 0 (0%)]

The current leading edge (i.e., latest work unit for which work has actually been sent out to a host) is n=8379831. The leading edge was at n=7870559 at the beginning of the challenge. Since the challenge started, the leading edge has advanced 6.47% as much as it had prior to the challenge!
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Time flies like an arrow. Fruit flies like a banana.

The results are final!

Throughout the 5 day challenge, we completed almost 300 thousand tasks. In addition to 3 new DIV primes -- one of them being the SECOND LARGEST known Fermat Divisor -- we also averaged about 10 times the subproject's typical LLR output.

134 teams and 688 individuals participated in the Challenge.

Top Three Individuals:
1. Gelly (who completed nearly a third of all challenge tasks)
2. Sean
3. tng

Top Three Teams:
1. Antarctic Crunchers
2. Czech National Team
3. Aggie The Pew

The next Challenge is the Tour de Primes, which starts Feb 1st. Hope everyone's 2021 is going smoothly so far!
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Time flies like an arrow. Fruit flies like a banana.