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Old 2019-10-10, 22:20   #1
mrh
 
"mrh"
Oct 2018
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Default Factoring M7777171

I'd like to factor 7777171, for no particular reason, other than I like the way it looks.
I threw some time at it, but it resists. What do you think would be best to try next? Just a bunch of ECM curves?

Last fiddled with by mrh on 2019-10-10 at 22:41
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Old 2019-10-10, 23:01   #2
petrw1
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"Wayne"
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Yes. You've done a lot of TF AND PM1.
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Old 2019-10-10, 23:05   #3
mrh
 
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Quote:
Originally Posted by petrw1 View Post
Yes. You've done a lot of TF AND PM1.
Thanks! How best to choose B1,B2? I'm not sure I understand the math for how to pick those based on PM1 work already done.
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Old 2019-10-10, 23:12   #4
petrw1
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https://www.mersenne.org/report_ecm/...1&ecm_hi=15000

Tells you how much is done/ remaining at each digit level.
I'd start with the lowest.: 50,000 (B2= 10x B1).
Run as many curves as you like.
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Old 2019-10-10, 23:28   #5
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Quote:
Originally Posted by petrw1 View Post
I'd start with the lowest.: 50,000 (B2= 10x B1).
Run as many curves as you like.
Maybe B2 = 100 × B1 is more suitable?
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Old 2019-10-11, 00:03   #6
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Quote:
Originally Posted by GP2 View Post
Maybe B2 = 100 × B1 is more suitable?
Oops my mistake.

Yes 100X
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Old 2020-09-09, 19:37   #7
gLauss
 
Nov 2014

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Default Factoring M20825573

I'm doing something similiar at the moment: Trying to find a factor for M20825573 in order to make up for my bad DC 11 years ago (which was one of my very first tests!).
I assume ECM is the way to go from now? Or should I increase P-1 again? Currently I'm running another ECM curve with B1=250000, B2=100*B1 and TF up to 75bits with mfaktc. However they take around 6 hours one, this is so long ... I might never find a factor :*(
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Old 2020-09-09, 20:28   #8
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Quote:
Originally Posted by gLauss View Post
I'm doing something similiar at the moment: Trying to find a factor for M20825573 in order to make up for my bad DC 11 years ago (which was one of my very first tests!).
I assume ECM is the way to go from now? Or should I increase P-1 again? Currently I'm running another ECM curve with B1=250000, B2=100*B1 and TF up to 75bits with mfaktc. However they take around 6 hours one, this is so long ... I might never find a factor :*(
Here is my suggestion:

1) Finish the TF to 75 bits - you'll have then put about 300 GPU GhzDays into TF.
2) One more P-1 attempt: B1 = 7,000,000, B2 = 200,000,000.
3) Complete the recommended set of 280 ECM curves at B1=50,000, B2 = 5,000,000.

Steps 2 and 3 are about 300 CPU GhzDays.

Note that each ECM curve gives you an independent chance of finding a factor. There's no point in increasing B1,B2 for ECM until you complete the recommended set of curves at the 25 digit level.

I estimate that steps 2 and 3 represent about 2 weeks of work for my Haswell i5 cpu. That's a lot of work to dedicate to one exponent. A quixotic quest, but one that I hope is fruitful for you.
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Old 2020-09-10, 10:03   #9
gLauss
 
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Quote:
Originally Posted by masser View Post
That's a lot of work to dedicate to one exponent. A quixotic quest, but one that I hope is fruitful for you.
Thanks, I know it's not useful and might sound strange, but I like the thrill of throwing a few ECM curves in-between a long boring PRP assignment. One can get a result after a short amount of time and you always have a - albeit little - chance of "success".

Also, it is the only exponent showing up as "bad" in my lifetime statistic. Previously there was also M21717953 in it, which I was able to move to the category "Factor found later" with P-1.

I probably won't do complete t25, but maybe 100 curves or so.

Last fiddled with by gLauss on 2020-09-10 at 10:08
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