[QUOTE=James Heinrich;523913]There was an issue that could exhibit this symptom that I should have resolved about 2 days ago. Are you reporting something from the recent past, or something that's still happening now?[/QUOTE]

It's in the six to seven second area now. I do not see this as an issue. :smile:

I took some chunks of exponents through mfaktc with bit levels 2 to 64 (since it's not significantly slower than 55 to 64) and Stages=0 to catch 'em all. Then I double checked against the export file of known factors. Weird luck, but the first chunks I did were all fully factored already (2900-2908 or so). Then I looked elsewhere, in the 2850-2851 million range, and wow, 2326 new factors. Of course, all were on exponents that had smaller factors found earlier. One chunk took about 1h 40min on an RTX 2080.

Should I continue? Just so that I'm not duplicating anyone else's effort or "stepping on toes" or whatever...

Also retested 2900-2901 for bit levels 64-67, mostly for fun. No new factors found as such, but I found out that mfaktc doesn't care if the factor found is prime. For example, M2900030879 has a factor 134562865615456511047, but that is 5800061759 * 23200247033, both of those are already in the database. 32 cases between 2900-2901.

[QUOTE=nomead;525468]I took some chunks of exponents through mfaktc with bit levels 2 to 64 (since it's not significantly slower than 55 to 64) and Stages=0 to catch 'em all.[/QUOTE]
While Stages=0 is fine and good for a large range of bits, I hope you also mean that you set StopAfterFactor=0 or else you won't catch 'em all.

[QUOTE=nomead;525468]Should I continue? Just so that I'm not duplicating anyone else's effort or "stepping on toes" or whatever... [/QUOTE]
Its a good a use as any for a GPU in my opinion :smile:
I would be surprised and very interested if you find anything below 55 bits, since I recently double checked all of this. But if the difference in compute time is negligible, a double/triple check doesn't hurt I suppose.

[QUOTE=nomead;525468]
Also retested 2900-2901 for bit levels 64-67, mostly for fun. No new factors found as such, but I found out that mfaktc doesn't care if the factor found is prime. For example, M2900030879 has a factor 134562865615456511047, but that is 5800061759 * 23200247033, both of those are already in the database. 32 cases between 2900-2901.
[/QUOTE]
I don't know a ton about the internal working of mfaktc, but I think if the smallest factor-of-a-factor is greater than your max sieve prime, its not going to catch the composite-ness in those cases.

Also, since each factor must be at least 2p+1 (k==1 at a minimum), this only becomes an issue when you factor past log2((2p+1)^2) ~= 2*(log2(p)+1) (64.866 for 2900)

Furthermore if a Mersenne number is divisible by the square of a prime, then you would have found a new Wieferich prime, which is highly improbable (but would be a monumental find!), so we can basically assume that k[SUB]1[/SUB] != k[SUB]2[/SUB]
So if k=1 for one of the factors, the next possible lowest other factor is k=4, then the actual limit is log2((2*p+1)*(2*4*p+1)) ~= 2*(log2(p)+2)
So for 2900M range, you won't find composite factors below 66.866 bits.

And looking at your example factor, that is exactly what you've found! (k=1 and k=4)

[QUOTE=nomead;525468]Should I continue? Just so that I'm not duplicating anyone else's effort or "stepping on toes" or whatever...[/QUOTE]In theory, [i]all[/i] factors below 2[sup]55[/sup] should be known. Beyond that, TF effort has usually been stopped after the first factor was found, so there's undoubtedly a lot of previously-unknown factors between 55-64 for exponents with one known factor in that range. By all means, submit whatever new factors you find, but please report here if you happen to find any [i]new[/i] factors smaller than 2[sup]55[/sup], since there shouldn't be any undiscovered ones.

If you have comprehensively TF'd a significant contiguous range to a fixed limit and not stopped after finding a factor (such that the range is fully checked up to the specified bit limit) you can please send me an email and I can update the fully-checked-TF limit for those exponents.

[QUOTE=hansl;525470]While Stages=0 is fine and good for a large range of bits, I hope you also mean that you set StopAfterFactor=0 or else you won't catch 'em all.[/QUOTE]
Whoops. Yes, of course, that too. Just forgot to mention it. :blush:

[QUOTE]I would be surprised and very interested if you find anything below 55 bits, since I recently double checked all of this. But if the difference in compute time is negligible, a double/triple check doesn't hurt I suppose.[/QUOTE]
Yeah, I would be surprised too. I had to measure the difference because I started doubting myself, and it seems that doing 55-64 is about 5% faster than 2-64. Maybe it's worth it after all to choose the narrower bit range, dunno.

[QUOTE=James Heinrich;525493]If you have comprehensively TF'd a significant contiguous range to a fixed limit and not stopped after finding a factor (such that the range is fully checked up to the specified bit limit) you can please send me an email and I can update the fully-checked-TF limit for those exponents.[/QUOTE]
Will do, when I have some bigger range to report.

Is mersenne.ca down? Haven't been able to access it today.

[QUOTE=kracker;525538]Is mersenne.ca down? Haven't been able to access it today.[/QUOTE]

Looks like it. Was about to ask the same question.

I concur: [url]https://downforeveryoneorjustme.com/mersenne.ca[/url]
isitdownrightnow .com agrees

It's just the front page that doesn't load, most other things that I tested seem to work fine.

It should be working fine now.

The site seems to be down again.