mersenneforum.org trial factoring of "small" mersenne numbers
 Register FAQ Search Today's Posts Mark Forums Read

 2003-07-15, 01:54 #1 antiroach     Jun 2003 24410 Posts trial factoring of "small" mersenne numbers i noticed that there are many "small" mersenne numbers that have only been trial divided upto 57 bits. (decomp -w 1 100000) for example. I tried to trial factor them (upto 58 bits) just for the heck of it but prime95 wouldnt let me. It said it was a bad factoring assignment. Anyone know why this is happening? Thanks.
 2003-07-15, 05:00 #2 NickGlover     Aug 2002 Richland, WA 2048 Posts I believe you need to set FactorOverride=58 in prime.ini . The reason you get "bad factoring assignment" is that default factoring depth for an exponent around 1 million is much lower than 57 bits, so Prime95 doesn't think there is any work to do on the exponent.
2003-07-15, 05:40   #3

"Richard B. Woods"
Aug 2002
Wisconsin USA

769210 Posts
Re: trial factoring of "small" mersenne numbers

Quote:
 Originally Posted by antiroach i noticed that there are many "small" mersenne numbers that have only been trial divided upto 57 bits. (decomp -w 1 100000) for example. I tried to trial factor them (upto 58 bits) just for the heck of it
I hope you're aware that trial-factoring a small Mnumber from 2^57 to 2^58 takes _longer_ than TFing a large Mnumber from 2^57 to 2^58, and that the ratio is roughly the inverse of the ratio of exponents. That is, it takes in the neighborhood of 100 times as long to TF 2^9xxxx-1 from 2^57 to 2^58 as it does to TF 2^9xxxxxx-1 from 2^57 to 2^58. That ratio is offset by a mildly faster TF iteration speed for the smaller Mnumber, but that offset is of a lower order than the exponent ratio.

 2003-07-15, 11:50 #4 eepiccolo     Dec 2002 Frederick County, MD 2×5×37 Posts Also, reference this post for another reason you shouldn't TF the smaller numbers. http://www.mersenneforum.org/viewtopic.php?t=415
 2003-07-15, 16:56 #5 antiroach     Jun 2003 22×61 Posts wow, thanks for all the replies. i did set factoroverride, but i had no idea that it takes longer to trial factor smaller numbers. I wasn't really planning on trial factoring those numbers since an first time LL and a double check were already performed on these numbers. I was just wondering why prime95 wouldn't even let me do it.
 2003-07-15, 17:50 #6 NickGlover     Aug 2002 Richland, WA 22·3·11 Posts I just tested to make sure and it does work. I randomly chose 944821 from the nofactor file. My worktodo.ini has Factor=944821,57 and I set FactorOverride=58 in prime.ini . Make certain to restart Prime95 after making changes to prime.ini .
 2003-07-16, 23:35 #7 antiroach     Jun 2003 24410 Posts i have only tested it upto 100,000. I havent bothered trying to trial factor anything above that. :)

 Similar Threads Thread Thread Starter Forum Replies Last Post ixfd64 Factoring 4 2012-10-16 04:07 cheesehead Math 6 2009-12-15 17:45 Jushi Factoring 2 2006-03-12 12:10 James Heinrich Software 1 2005-04-10 02:44 James Heinrich Marin's Mersenne-aries 8 2004-05-17 11:09

All times are UTC. The time now is 15:29.

Tue Jan 19 15:29:37 UTC 2021 up 47 days, 11:40, 0 users, load averages: 1.37, 1.54, 1.51