mersenneforum.org Factoring M7777171
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 2019-10-10, 22:20 #1 mrh   "mrh" Oct 2018 Temecula, ca 3716 Posts 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
 2019-10-10, 23:01 #2 petrw1 1976 Toyota Corona years forever!     "Wayne" Nov 2006 Saskatchewan, Canada 104438 Posts Yes. You've done a lot of TF AND PM1.
2019-10-10, 23:05   #3
mrh

"mrh"
Oct 2018
Temecula, ca

5·11 Posts

Quote:
 Originally Posted by petrw1 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.

 2019-10-10, 23:12 #4 petrw1 1976 Toyota Corona years forever!     "Wayne" Nov 2006 Saskatchewan, Canada 41·107 Posts 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.
2019-10-10, 23:28   #5
GP2

Sep 2003

1010000101002 Posts

Quote:
 Originally Posted by petrw1 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?

2019-10-11, 00:03   #6
petrw1
1976 Toyota Corona years forever!

"Wayne"
Nov 2006

41×107 Posts

Quote:
 Originally Posted by GP2 Maybe B2 = 100 × B1 is more suitable?
Oops my mistake.

Yes 100X

 2020-09-09, 19:37 #7 gLauss   Nov 2014 3 Posts 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 :*(
2020-09-09, 20:28   #8
masser

Jul 2003

143510 Posts

Quote:
 Originally Posted by gLauss 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.

2020-09-10, 10:03   #9
gLauss

Nov 2014

3 Posts

Quote:
 Originally Posted by masser 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