Added [URL="https://t5k.org/primes/page.php?id=135795"]135795[/URL] : 421*2^23243751 (699710 digits)

Max found:
909*2^20569371 is prime 
[url='https://t5k.org/primes/page.php?id=135805']909*2^20569371[/url] seems composite but verification status is PRP.

[QUOTE=kar_bon;626979][url='https://t5k.org/primes/page.php?id=135805']909*2^20569371[/url] seems composite but verification status is PRP.[/QUOTE]
I just now doublechecked it. LLR version 3.8.23 says otherwise: 909*2^20569371 is prime! (619203 decimal digits) Time : 1299.213 sec. Max's machines have been quite stable. He just now found another prime and I also verified that it is prime. I'll report it in the next post. The new top5000 site appears to be wrong! They need to work on their verification process. It takes many hours for the tests to start, it takes too long to run the test (over an hour for this one), and now it outputs the wrong result. Anyone else care to test this? Edit: I just now used their "let us know if anything isn't working" process to Email them about the problem. 
Max found:
813*2^20603921 is prime Doublechecked by LLR 3.8.23. 
[QUOTE=gd_barnes;626984]I just now doublechecked it. LLR version 3.8.23 says otherwise:
909*2^20569371 is prime! (619203 decimal digits) Time : 1299.213 sec. Max's machines have been quite stable. He just now found another prime and I also verified that it is prime. I'll report it in the next post. The new top5000 site appears to be wrong! They need to work on their verification process. It takes many hours for the tests to start, it takes too long to run the test (over an hour for this one), and now it outputs the wrong result. Anyone else care to test this? Edit: I just now used their "let us know if anything isn't working" process to Email them about the problem.[/QUOTE] Could be a hardware glitch on the Digital Ocean cloud ressource used by the new t5k.org. The prime is most likely good. Administrators of t5k.org are aware and have up to now prevented the deletion of the entry. Note that a proof of such c=1 candidate with LucasLehmerRiesel does not allow Gerbicz checks to catch hardware glitches. So the best way to prove primality seems to be to repeat the run on several different [I]reliable[/I] machines. /JeppeSN 
[QUOTE=JeppeSN;626986]Could be a hardware glitch on the Digital Ocean cloud ressource used by the new t5k.org. The prime is most likely good. Administrators of t5k.org are aware and have up to now prevented the deletion of the entry.
Note that a proof of such c=1 candidate with LucasLehmerRiesel does not allow Gerbicz checks to catch hardware glitches. So the best way to prove primality seems to be to repeat the run on several different [I]reliable[/I] machines. /JeppeSN[/QUOTE] Thanks for the update and info! 
[QUOTE=gd_barnes;626984]I just now doublechecked it. LLR version 3.8.23 says otherwise:
909*2^20569371 is prime! (619203 decimal digits) Time : 1299.213 sec. Anyone else care to test this?[/QUOTE] I also verified it. C:\prpnet\prpclient4>cllr64.exe v LLR Program  Version 3.8.23, using Gwnum Library Version 29.8 C:\prpnet\prpclient4>cllr64.exe t4 d q"909*2^20569371" Starting Lucas Lehmer Riesel prime test of 909*2^20569371 Using AVX FFT length 140K, Pass1=448, Pass2=320, clm=1, 4 threads V1 = 3 ; Computing U0...done. 909*2^20569371 is prime! (619203 decimal digits) Time : 1001.568 sec. Regards Odi 
I ran it using my copy of PFGW (which appears to be the same version as T5K), and I got a bunch of roundoff errors:
[code]$ ./pfgw tp q"909*2^20569371" PFGW Version 4.0.1.64BIT.20191203.x86_Dev [GWNUM 29.8] Primality testing 909*2^20569371 [N+1, BrillhartLehmerSelfridge] Running N+1 test using discriminant 5, base 1+sqrt(5) Detected in MAXERR>0.45 (round off check) in Exponentiator::Iterate Iteration: 18/2056948 ERROR: ROUND OFF 0.5>0.45 (Test aborted, try again using the a1 switch) Running N+1 test using discriminant 5, base 1+sqrt(5) Detected in MAXERR>0.45 (round off check) in Exponentiator::Iterate Iteration: 19/2056948 ERROR: ROUND OFF 0.5>0.45 (Test aborted, try again using the a2 (or possibly a0) switch) Running N+1 test using discriminant 5, base 1+sqrt(5) ^C1: 909*2^20569371 5000/2056948 mro=0.5 CtrlC detected, shutting down the program. [/code] I reran with [c]a2[/c]: [code]$ ./pfgw tp q"909*2^20569371" a2 PFGW Version 4.0.1.64BIT.20191203.x86_Dev [GWNUM 29.8] Primality testing 909*2^20569371 [N+1, BrillhartLehmerSelfridge] Running N+1 test using discriminant 5, base 1+sqrt(5) 909*2^20569371 is prime! (3940.2488s+0.0006s) [/code] 
The bad result on t5k.org is reproducible, so not a random hardware glitch.
Thought to be related to the version of GWNUM used, on hardware where the AVX512 instructions [I]are[/I] available. If someone with some version of PFGW can test on AVX512capable hardware, with [C]tp q"909*2^20569371" V[/C] where the V seems to give info about choices made by GWNUM. /JeppeSN 
[CODE]$ ./pfgw64 tp q"909*2^20569371" V
PFGW Version 4.0.4.64BIT.20221214.x86_Dev [GWNUM 30.11] Primality testing 909*2^20569371 [N+1, BrillhartLehmerSelfridge] Running N+1 test using discriminant 5, base 1+sqrt(5) Special modular reduction using AVX512 FFT length 144K, Pass1=192, Pass2=768, clm=1 on 909*2^20569371 909*2^20569371 is prime! (1746.6204s+0.0004s)[/CODE] 
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