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Old 2008-04-20, 23:27   #1
robo_mojo
 
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Mar 2008

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Default Dumb question about missing srsieve factors

Greetings,

I run a command such as:
Code:
$ srsieve -f -N 500000 -P 10000000 "561179*2^n+1"
It prints out a lot of factors and writes them to srfactors.txt. And at the end it prints:
Code:
Sieving 3 <= p <= 10000000 eliminated 484614 terms, 15387 remain.
Wrote 15387 terms for 1 sequence to srsieve format file `srsieve.out'.
srsieve stopped: at p=10000000 because --pmax was reached.
It says it eliminated 484614 terms, but there are only 6171 terms with factors in srfactors.txt:
Code:
$ wc -l srfactors.txt
6171 srfactors.txt
I was rather expecting to have a srfactors.txt file with factors for 484614 terms.

So my dumb question (I'm sure) is: What happened to the other terms?

Last fiddled with by robo_mojo on 2008-04-20 at 23:28
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Old 2008-04-20, 23:48   #2
axn
 
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Quote:
Originally Posted by robo_mojo View Post
What happened to the other terms?
HINT:- What is the smallest factor recorded in srfactors.txt?

Last fiddled with by axn on 2008-04-20 at 23:48 Reason: speeling
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Old 2008-04-21, 00:02   #3
robo_mojo
 
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Quote:
Originally Posted by axn1 View Post
HINT:- What is the smallest factor recorded in srfactors.txt?
I told ya it was a dumb question :)
Code:
100069 | 561179*2^15071+1
So I take it the other terms have (trivially) small factors less than 10^5 and they don't get printed...

Well now that's cleared up.
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Old 2008-04-22, 03:51   #4
geoff
 
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Quote:
Originally Posted by robo_mojo View Post
So I take it the other terms have (trivially) small factors less than 10^5 and they don't get printed...
You can use the -m switch if you really want the small factors: `srsieve -m X ...' will cause factors less than X not to be recorded. X=100,000 is the default.

The reason for not recording small factors by default is that it usually takes much longer to write small factors to file (or even just print them to the screen) than it takes to find them in the first place.

Last fiddled with by geoff on 2008-04-22 at 03:52
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Old 2008-04-22, 04:37   #5
robo_mojo
 
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Quote:
Originally Posted by geoff View Post
You can use the -m switch if you really want the small factors: `srsieve -m X ...' will cause factors less than X not to be recorded. X=100,000 is the default.

The reason for not recording small factors by default is that it usually takes much longer to write small factors to file (or even just print them to the screen) than it takes to find them in the first place.
Thanks for the info. It makes sense to only print large factors.
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