20161101, 14:09  #1 
"John A Burroughs"
Jan 2016
Warwick, RI
25_{10} Posts 
F12 factor found?
Hi,
I was running ECM curves on F12 and my prime log states: F12 has a factor: 45477879701734570611058964078361695337745924097 but when I enter that in my factor into my worktodo.txt for future curves, I get the message "45477879701734570611058964078361695337745924097 does not divide F12" Did I find a factor? Thanks, John 
20161101, 14:12  #2 
(loop (#_fork))
Feb 2006
Cambridge, England
2·7·461 Posts 
You found a factor, but it is a composite factor
Code:
114689 * 26017793 * 63766529 * 190274191361 * 1256132134125569 
20161101, 14:23  #3 
"John A Burroughs"
Jan 2016
Warwick, RI
19_{16} Posts 
My worktodo.txt contains:
ECM2=N/A,1,2,4096,1,999999999,99999999900,10,"114689,26017793,63766529,190274191361,1256132134125569,568630647535356955169033410940867804839360742060818433" I blocked out my reservation code and replaced it with N/A. I will still get composite factors? Thanks, John 
20161101, 16:41  #4  
Sep 2003
2·5·7·37 Posts 
Quote:
So it doesn't actually divide out the known factors, rather it merely ignores them. Last fiddled with by GP2 on 20161101 at 16:41 

20161101, 16:44  #5 
Sep 2003
A1E_{16} Posts 
If your ECM2 line contains a doublequoted string with commaseparated known factors at the end, then it should never report any bogus composite factors that are composed of the alreadyknown prime factors.
It's not clear what happened, but maybe at some point you inadvertently added an ECM2 line to your worktodo.txt that was missing the doublequoted string at the end. 
20161101, 23:38  #6  
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
3^{3}×13×29 Posts 
Quote:
When the code parses an assignment, it goes word by word. It prepares the FFT structures for F12 and a standalone long number m=F12; then it divides m by every word and skips those that don't divide (and at this point when it reports "X doesn't divide F12" it means X doesn't divide "X doesn't divide F12/product(all factors before X)". So if you put one factor in the dquotes twice, the code will complain about the second of them but will work just fine as intended. If you put "(a)", "(product of b*c)" and also "(product of a*c)", one after another in dquotes, you will get an error "(a*c) doesn't divide F12" but the code will still work as if you provided a, b and c. You can also provide a product of all factors in dquotes  that will be also fine. 

20161101, 23:57  #7 
Sep 2003
2×5×7×37 Posts 
Ah, OK.
On a different note: we've twice had Mersenne primes discovered without anyone noticing for months, because the automatic notification failed. I wonder if there is any notification mechanism if new Fermat factors are found, and are we sure it works? Is it possible that some Fermat factor was found but has been sitting forgotten in a log file somewhere... 
20161102, 01:00  #8 
P90 years forever!
Aug 2002
Yeehaw, FL
2×4,127 Posts 
There is no email notifications for Fermat factors. The good news is they aren't hidden. They should get added to the database and displayed for all to see.

20161102, 02:04  #9  
Sep 2003
2·5·7·37 Posts 
Quote:
And assuming you can actually see them somewhere, is anyone viewing that periodically and checking for new ones? Last fiddled with by GP2 on 20161102 at 02:06 

20161102, 04:37  #10 
P90 years forever!
Aug 2002
Yeehaw, FL
2·4,127 Posts 
I guess the only place to see them is to get an ECM assignment.
I checked and there are no new ones. Vang's F12 factor was missing. 
20161102, 13:54  #11 
Aug 2002
2×7×617 Posts 

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