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Old 2003-07-15, 01:54   #1
antiroach
 
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Default 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.
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Old 2003-07-15, 05:00   #2
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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.
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Old 2003-07-15, 05:40   #3
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Default 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.
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Old 2003-07-15, 11:50   #4
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Also, reference this post for another reason you shouldn't TF the smaller numbers.

http://www.mersenneforum.org/viewtopic.php?t=415
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Old 2003-07-15, 16:56   #5
antiroach
 
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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.
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Old 2003-07-15, 17:50   #6
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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 .
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Old 2003-07-16, 23:35   #7
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i have only tested it upto 100,000. I havent bothered trying to trial factor anything above that. :)
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