20031216, 18:11  #1 
22EC_{16} Posts 
P1 factoring Q&A thread
After completing the P1 test, the program started testing for GCD. I got this result:
Code:
Stage 1 GCD complete. Time: 492.051 sec. Not enough memory available to run stage 2 now. Will try again at a later time. Starting Primality test of M[...] 
20031216, 18:26  #2 
P90 years forever!
Aug 2002
Yeehaw, FL
7,351 Posts 
This is normal and nothing to worry about. Stage 2 will run at night when you have told prime95 it can use more memory. In the meantime, it will start the LucasLehmer test assuming that stage 2 won't find a factor (about a 2% chance).

20031220, 11:29  #3 
13355_{8} Posts 
Do you mean a 98 percent chance?

20031220, 16:33  #4 
P90 years forever!
Aug 2002
Yeehaw, FL
7,351 Posts 
Oops. Right, a 98% chance it won't find a factor.

20050310, 13:42  #5 
"Kyle"
Feb 2005
Somewhere near M52..
2^{2}×227 Posts 
Chances
A couple quick questions. I'm currently testing an exponent that will yield a 10,300,000+ digit prime. It is currently 91.35% done with Stage 1 LL. Since it has not found a factor yet, what are the odds that it is prime? Also, since I don't think I have enough memory to do Stage2, who will do that and who will get creditshould the number turn out to be prime. (not to be stingy, but I wouldn't mind collecting the $50,000 )
Thanks. Kyle 
20050310, 13:54  #6 
Jul 2004
Potsdam, Germany
33F_{16} Posts 
When you do a Stage1, you don't do a LL test, but P1 factoring.
As a result, you can only find factors with this test (and thus prove the number nonprime). A LL test is done after Stage2 of P1 factoring (which can even done with ~20 MB RAM  with lower bounds and hence less chance of success, though). Concerning the chances, they are said to be near 1/250,000  depending on factoring attempts already done for that number. So, every completed LL test gives you $0.20 in average (mean value). 
20050310, 13:54  #7 
Jan 2005
Singapore
D_{16} Posts 
If you go to "Test > Status" you will get a popup window telling you the chances that your exponent will yield a prime.
As for the second question, I don't know who gets assigned those doublechecks when a prime is found, but if you find that it is a prime and the double (or triple) check verifies that is the case you should receive the credit. Only if you find erroneously that it is a prime and the double check makes this clear you would lose the credit for the discovery (which is fair enough, anyway). At least that is my understanding. Someone please correct me if that is wrong! [edited] ooops! Mystwalker just gave you a better answer and beat me by a millisecond or so [/edited] Last fiddled with by blackguard on 20050310 at 13:55 
20050310, 14:15  #8 
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
2^{3}·7·167 Posts 
If you are doing the P1 factoring, you are not proving the number to be prime, you are rather looking for a factor to disprove its primeness. Because, you can't find a prime with P1, you don't get credit as having found it, therefore you don't share as a discoverer.
If you are doing the LL primality checking, you do get credit. To answer blackguard's question about double checking: To ensure that a newly discovered prime is real, Geogre has some volunteers that have access to nonx86 computers that are fast to do double checking. 
20050310, 21:46  #9 
"Kyle"
Feb 2005
Somewhere near M52..
908_{10} Posts 
Okay thanks. That answers about half of the question. I know you can go to test and status to find out the chances. My question though is since the program is now nearly 92% done with Stage1, how much have the odds improved? And another question. For an exponent of this size, what is the ideal memory size needed? Thanks.

20050310, 22:56  #10  
Jul 2004
Potsdam, Germany
3·277 Posts 
P1 factoring and LL testing won't have a result until they have completed (with P1, some factors can already be found after stage1). Hence, the current status doesn't enhance your chances compared to before the beginning of P1 factoring. After P1 factoring (stage1 as well as stage2), the chances increase  but I don't know the exact values. Maybe one or two percent...
Concerning the memory requirements for P1 factoring, there is a table in the readme file of prime95: Quote:
So, contrary to my guess above, 65MB are the minimum for a number of that size. 

20050310, 23:43  #11  
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
2^{3}·7·167 Posts 
Quote:


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