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 2015-05-03, 10:38 #1 Gordon     Nov 2008 50710 Posts Double Factors I've run a few ranges up in the hundreds of millions and on three occasions have had mfaktc return two factors for the same exponent. For the first time today I have had the same in the "normal" work-space, a 40m double check in fact. UID: nitro/GTX-970, M40553413 has a factor: 4628777451145663818113 [TF:71:72:mfaktc 0.21 barrett76_mul32_gs] UID: nitro/GTX-970, M40553413 has a factor: 2957800359711131127671 [TF:71:72:mfaktc 0.21 barrett76_mul32_gs] UID: nitro/GTX-970, found 2 factors for M40553413 from 2^71 to 2^72 [mfaktc 0.21 barrett76_mul32_gs] How often should we expect this to arise? In other words is this a rare event? For interest here are the others UID: nitro/NVidia, M374011241 has a factor: 255127733487162275449 [TF:66:69:mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, M374011241 has a factor: 374875803406924157593 [TF:66:69:mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, found 2 factors for M374011241 from 2^66 to 2^69 [mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, M800074609 has a factor: 278430345631804693927 [TF:66:68:mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, M800074609 has a factor: 201002749157149138999 [TF:66:68:mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, found 2 factors for M800074609 from 2^66 to 2^68 [mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, M800079893 has a factor: 87320074164777027913 [TF:66:68:mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, M800079893 has a factor: 107522046708157973279 [TF:66:68:mfaktc 0.20 barrett76_mul32_gs] UID: nitro/NVidia, found 2 factors for M800079893 from 2^66 to 2^68 [mfaktc 0.20 barrett76_mul32_gs]
 2015-05-03, 13:01 #2 VictordeHolland     "Victor de Hollander" Aug 2011 the Netherlands 32×131 Posts It depends on your settings in mfaktc/mfakto config: Code: # possible values for StopAfterFactor: # 0: Do not stop the current assignment after a factor was found. # 1: When a factor was found for the current assignment stop after the # current bitlevel. This makes only sense when Stages is enabled. # 2: When a factor was found for the current assignment stop after the # current class. # # Default: StopAfterFactor=2 If you choose the default (StopAfterFactor=2), you will find them extremely rarely. Option 1 will occasionally find 2 (or more) factors in a bitlevel. With option 0, your GPU will do all the assigned bitlevels even if a factor is found (and thus has a chance to find another factor at a higher bitlevel). Note: for the progress of finding Mersenne Primes, finding a single factor rules that exponent out of being prime. It depends on your view if you want to complete the current bitlevel after a factor is found. I 'understand' a trial factoring assignment as: trial factor from x bits until a factor is found (success) or y bits (assignment complete). Some people complete the current bitlevel for clearness/tidiness/clarity (or just want to have some fun with finding multiple factors). Last fiddled with by VictordeHolland on 2015-05-03 at 13:15
2015-05-03, 18:28   #3
xilman
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May 2003
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Quote:
 Originally Posted by VictordeHolland ISome people complete the current bitlevel for clearness/tidiness/clarity (or just want to have some fun with finding multiple factors).
And some people have fun finding factors rather than finding Mersenne primes. I've been in this class for a very long time now.

It takes all sorts.

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