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 2008-10-13, 00:52 #1 MooooMoo Apprentice Crank     Mar 2006 11·41 Posts Sophie Germains, multiple n-ranges, future of TPS This thread is for discussing a possible search for Sophies and searching a range of both n and k for twins. Recently, a couple of people have asked me about doing a search for both sophies and twins for n=500K. Doing so means that there's a greater chance of finding either a sophie or a twin, but one problem is that the chance of finding a twin in a range decreases the higher you sieve. As a guide, there are about 500,000 candidates left after triple-sieving a range of 10G to p=1T. Continuing to p=1000T with a twin-sieve would leave 320,000 candidates remaining, while continuing to p=1000T with a triple-sieve would leave only 256,000 candidates remaining. Some of those candidates eliminated with a triple sieve but not eliminated with a twin sieve may have been twins. Another suggested idea came up in this rather long thread: http://www.mersenneforum.org/showthread.php?t=8479 It was suggested that TPS search for a range of n with a smaller k range instead of searching a large k-range with a fixed n. The advantage is that the low k-candidates in a variable n-range are faster to test than those with a fixed n, while a disadvantage is that sieving won't be as efficient. If you want TPS to also look for sophies, I'd welcome suggestions for a suitable k-range for triple sieving n=500K. For those who want to try triple-sieving a test range to get the idea of how it works and how much time and RAM is required, download David Underbakke's Twingen software at: http://www.sendspace.com/file/261wdk
2008-10-14, 14:40   #2
mdettweiler
A Sunny Moo

Aug 2007
USA (GMT-5)

141418 Posts

Quote:
 Originally Posted by MooooMoo This thread is for discussing a possible search for Sophies and searching a range of both n and k for twins. Recently, a couple of people have asked me about doing a search for both sophies and twins for n=500K. Doing so means that there's a greater chance of finding either a sophie or a twin, but one problem is that the chance of finding a twin in a range decreases the higher you sieve. As a guide, there are about 500,000 candidates left after triple-sieving a range of 10G to p=1T. Continuing to p=1000T with a twin-sieve would leave 320,000 candidates remaining, while continuing to p=1000T with a triple-sieve would leave only 256,000 candidates remaining. Some of those candidates eliminated with a triple sieve but not eliminated with a twin sieve may have been twins. Another suggested idea came up in this rather long thread: http://www.mersenneforum.org/showthread.php?t=8479 It was suggested that TPS search for a range of n with a smaller k range instead of searching a large k-range with a fixed n. The advantage is that the low k-candidates in a variable n-range are faster to test than those with a fixed n, while a disadvantage is that sieving won't be as efficient. If you want TPS to also look for sophies, I'd welcome suggestions for a suitable k-range for triple sieving n=500K. For those who want to try triple-sieving a test range to get the idea of how it works and how much time and RAM is required, download David Underbakke's Twingen software at: http://www.sendspace.com/file/261wdk
I for one am highly in favor of the smaller k-range, variable n-range idea, and would be sure to find some CPU time to throw on it if TPS chooses to go that route.

(Anyway, just my \$0.02. I know I haven't really contributed much to this project besides a bunch of PrimeGrid TPS WU's a while back, so I guess my vote may not count as much as others'. )

 2008-10-29, 17:17 #3 Skligmund     Dec 2006 Anchorage, Alaska 4E16 Posts I actually like the idea of doing multiple n small k range just above n=195000. I would like to see the feasablity of doing this. Can it be adapted to primegrid somehow? Assuming n=333333 stalls out or something, there might be interest in the possibility of a record with the smaller n's. I personally have lost any real interest in n=333333. I get htis feeling of 'going to take forever' to find the twin. Again, I'd like to see a much larger prime, but with a lower n value, we could do a lot of work in less time to check feasablity for going higher. Thoughts?
 2008-10-29, 20:35 #4 Flatlander I quite division it     "Chris" Feb 2005 England 31·67 Posts To save repitition of work, I have searched for twins from n=195,032 to 201,700(ish), k from 1003 to 124751. (I think I missed two ranges of n of size 8.) I found about 150 Riesels but no twins. (Obviously!) It took about 3 months of all 4 C2Q cores at 3.18GHz, including sieving. I am no longer searching below top-5000 level. Last fiddled with by Flatlander on 2008-10-29 at 20:38
2008-10-29, 21:10   #5
MooooMoo
Apprentice Crank

Mar 2006

1C316 Posts

Quote:
 Originally Posted by Skligmund I actually like the idea of doing multiple n small k range just above n=195000. I would like to see the feasablity of doing this. Can it be adapted to primegrid somehow? Assuming n=333333 stalls out or something, there might be interest in the possibility of a record with the smaller n's. I personally have lost any real interest in n=333333. I get htis feeling of 'going to take forever' to find the twin. Again, I'd like to see a much larger prime, but with a lower n value, we could do a lot of work in less time to check feasablity for going higher. Thoughts?
I've posted a sieve file for you since you were interested in doing a multiple n, small k range. It tests n=197000-197009 from k=1-1M. It should be slightly faster to test than n=195000 because of the small k's.

The sieve file hasn't been sieved deeply (only to p=250G) because each n must be sieved separately and because the k range is so small. At p=250G, 1 k is eliminated every 30-40 seconds, while it takes slightly less than a minute to LLR them.

This search for twins a bit above n=195000 might be adapted to Primegrid, but I'll wait until n=333333 is done first.
Note: The file now excludes all k below 124,000 since Flatlander LLR'ed it already.
Attached Files
 197000-197009.txt (74.6 KB, 198 views)

Last fiddled with by MooooMoo on 2008-10-29 at 21:12

 2008-10-30, 00:02 #6 Skligmund     Dec 2006 Anchorage, Alaska 1168 Posts Alright. I'll download that as soon as I get home and play with it. Thanks!
 2008-11-05, 08:37 #7 Cybertronic     Jan 2007 DEUTSCHLAND ! 3×89 Posts Hello, is prping of 197000-197009.txt complete ? primes known ? I will try to find fast any primes with my selection methode. best
2008-11-05, 12:17   #8
Cybertronic

Jan 2007
DEUTSCHLAND !

3·89 Posts

Quote:
 Originally Posted by Cybertronic I will try to find fast any primes with my selection methode.
Hm, it works fine .

The first prime "987975*2^197002-1 is prime!"

Last fiddled with by Cybertronic on 2008-11-05 at 12:18

 2008-11-05, 15:03 #9 Cybertronic     Jan 2007 DEUTSCHLAND ! 3·89 Posts No joke , I select n=200065 , sieved with Newpgen all k's from 125000 to 1M 3 minutes and start my 4 tasks. After 2 minutes I found "830535*2^200065-1 is prime! Time : 86.763 sec." I wonder how easy it is to find so large primes :-)

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