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Old 2014-05-12, 21:04   #1
Batalov
 
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Phi(4,2^7658614+1)/2

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Default 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
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Old 2014-05-13, 13:09   #2
swellman
 
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Yafu can sieve this form too.
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Old 2014-05-13, 13:45   #3
bsquared
 
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It can?
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Old 2014-05-13, 14:12   #4
LaurV
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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
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Old 2014-05-13, 14:17   #5
swellman
 
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Quote:
Originally Posted by bsquared View Post
It can?
You mean it can't? I thought Yafu did everything.

I stand corrected - Yafu can factor this form via SNFS.
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Old 2014-05-13, 14:46   #6
bsquared
 
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Quote:
Originally Posted by swellman View Post
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.
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Old 2014-05-13, 17:54   #7
Batalov
 
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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
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Old 2014-05-13, 19:01   #8
XYYXF
 
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Quote:
Originally Posted by Batalov View Post
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 :-)
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Old 2014-05-13, 19:08   #9
Batalov
 
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Multisieve reversed that order (because xy > yx, for 3<=x<y, and because it sieves for xy +/- yx, so it would be convenient to have a positive number). It was an example of setting up Multisieve. Multisieve will require x<y.

Let's start the fun?
I will run the [20001-40000, 11-200] range. Found six new PRPs so far, while warming up.
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Old 2014-05-13, 19:19   #10
XYYXF
 
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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].
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Old 2014-05-13, 22:28   #11
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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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