## Other

drummers-lowrise

Message boards : Proth Prime Search : Factors=Primes?

 Subscribe SortOldest firstNewest firstHighest rated posts first
Author Message
trigggl

Joined: 24 Feb 09
Posts: 57
ID: 36070
Credit: 30,388,836
RAC: 0

Message 16365 - Posted: 20 Jun 2009 | 15:24:46 UTC

I've noticed on my past two pps sieve tasks that in the slots folder I'll have a file called "factors.txt". The first task had four factors in it and my second had at least one. Are factors primes or just possible primes? If they are primes how long would it take them to show up on my account page?

Volunteer developer

Joined: 11 Sep 08
Posts: 580
ID: 28785
Credit: 263,498,026
RAC: 0

Message 16366 - Posted: 20 Jun 2009 | 15:41:15 UTC - in response to Message 16365.

Since you are running sieve those are only possible primes.
It is - so to speak - the remnant of all you have sieved with the corresponding WU.

[SG]Puzzle-Peter
Volunteer tester

Joined: 14 Jun 08
Posts: 374
ID: 24128
Credit: 92,652,187
RAC: 0

Message 16367 - Posted: 20 Jun 2009 | 15:55:05 UTC - in response to Message 16366.
Last modified: 20 Jun 2009 | 15:58:43 UTC

The purpose of sieving is to reduce the number of candidates that have to be primality checked by finding factors for those candidates. A factor is a number which divides a candidate.

So if you found 4 factors in one PPS sieve WU, you showed that 4 of the candidates in the sieve file are composite. They will be deleted from the sieve file and when it's time for the primality tests, they will not be tested because we already know they are not prime.

What you did is rather the "opposite" of finding a prime. When a new range of numbers gets worked on, sieving is much more efficient than primality testing E.g. one primality test might last 8 minutes, but 8 minutes of sieving might find 3 factors. So sieving reduces the number of remaining candidates faster than primality testing. As more and more candidates are removed, sieving finds factors less quickly, until it's less effective than testing every remaining candidate.This is the time to switch methods. But you'll never find a prime via sieving.

I'm not running a sieve right now so I can't copy a line, but you'll find something which looks like this in the factor file:

152374867 | 2756*2^487533

That means that 152374867 is a factor of 2756*2^487533, so we know that 2756*2^487533 is not prime.
____________
There are only 10 kinds of people - those who understand binary and those who don't

trigggl

Joined: 24 Feb 09
Posts: 57
ID: 36070
Credit: 30,388,836
RAC: 0

Message 16378 - Posted: 21 Jun 2009 | 3:29:24 UTC - in response to Message 16367.

Obviously, I forgot what a factor is. Is it too late to change the title of the thread? Thanks for the explanation. I don't know what I was thinking.

So basically I don't want any factors, though the factor itself could be a prime like 2 out of 4.

I'm awake now.

I guess I'll continue to sieve for now. I did after all request it.

thommy3

Joined: 7 Jan 08
Posts: 42
ID: 17265
Credit: 268,651
RAC: 0

Message 16384 - Posted: 21 Jun 2009 | 7:16:17 UTC - in response to Message 16378.

With the small factors we are testing here, basically 100% of the found factors are prime. But those are uninterrestingly small, they don't get listed on the account pages.

Yusup

Joined: 15 May 09
Posts: 122
ID: 40081
Credit: 3,188,593
RAC: 0

Message 20681 - Posted: 31 Jan 2010 | 7:52:30 UTC - in response to Message 16384.

But are those important as such?

Message boards : Proth Prime Search : Factors=Primes?