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 2014-05-12, 21:04 #1 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 2·11·457 Posts Leyland Primes (x^y+y^x primes) Placeholder for xy+yx prime search reservations. Contact XYYXF to reserve a range. Multisieve is one of the sieve programs capable of sieving this form. Last fiddled with by XYYXF on 2015-02-02 at 15:03
 2014-05-13, 13:09 #2 swellman     Jun 2012 384810 Posts Yafu can sieve this form too.
 2014-05-13, 13:45 #3 bsquared     "Ben" Feb 2007 22×3×311 Posts It can?
 2014-05-13, 14:12 #4 LaurV Romulan Interpreter     "name field" Jun 2011 Thailand 19·541 Posts Sorry, I don't laugh at any of you. It is just about the situation, I expected all in the world but didn't expect Ben's reply to this, in this way! [edit: if some guest read this, maybe they don't know, Ben is yafu's author]. I can't stop laughing. Last fiddled with by LaurV on 2014-05-13 at 14:14
2014-05-13, 14:17   #5
swellman

Jun 2012

23·13·37 Posts

Quote:
 Originally Posted by bsquared It can?
You mean it can't? I thought Yafu did everything.

I stand corrected - Yafu can factor this form via SNFS.

2014-05-13, 14:46   #6
bsquared

"Ben"
Feb 2007

22×3×311 Posts

Quote:
 Originally Posted by swellman You mean it can't? I thought Yafu did everything. I stand corrected - Yafu can factor this form via SNFS.
Err, well, yes, of course it can do everything, except for LaurV's loops and ifs

Yep, you were probably thinking of SNFS factorization.

 2014-05-13, 17:54 #7 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 1005410 Posts Well, of course, sieving can be done with almost any program (including your own). But the question is how fast can it sieve. Multisieve is good. A worked example: 1. Get Multisieve and PFGW 2. Start, select x^y+-y^x mode, select "+", set up some names for outputs, e.g. "xyyx200.out" and "xyyx200.log"; set up limits above previously searched: e.g. x from 200 to 200, y from 20001 to 30000 3. Sieve, after a while, stop (e.g. at 10-20s per candidate) 4. Run pfgw on the "xyyx200.out" file (with -f0 -l) 5. ... 6. PROFIT! e.g. 200^20373+20373^200 is a (new) PRP 7. Submit to PRP top
2014-05-13, 19:01   #8
XYYXF

Jan 2005
Minsk, Belarus

24×52 Posts

Quote:
 Originally Posted by Batalov e.g. x from 200 to 200, y from 20001 to 30000
Conventionally x is always greater than y, and it's also recommended to test all y's for a given x :)

So it's better to take e.g. x from 12501 to 13000, y from 2001 to 12999 :-)

 2014-05-13, 19:08 #9 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 2·11·457 Posts Multisieve reversed that order (because xy > yx, for 3<=x
 2014-05-13, 19:19 #10 XYYXF     Jan 2005 Minsk, Belarus 24·52 Posts OK, http://xyyxf.at.tut.by/primes.html#ranges is updated. But I still hope someone will decrease the number of steps y>10, y>200, y>1000, y>2000 :-) E.g. it's possible to take [15001-20000, 1001-2000].
 2014-05-13, 22:28 #11 rogue     "Mark" Apr 2003 Between here and the 2·592 Posts I haven't touched MultiSieve in years. It's good to know that some people still have use for it. After looking at the code (talk about a blast from the past), I think it would be easy to convert this sieve to OpenCL since it doesn't use a discrete log. An OpenCL version might 100x faster.

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