20050510, 16:04  #1 
May 2003
11000001011_{2} Posts 
Large small factor
I just found my first decent sized factor using ECM. It's a 44 digit probable prime factor coming from 16651^131. (It's one of the composites on the OPN website.)
Just wanted to share my joy. :) 
20050510, 16:21  #2  
Nov 2003
2^{2}×5×373 Posts 
Quote:
Huh???? (16651^13 1)/16650 is itself only 51 digits...... It is divisible by 30187, leaving a composite of only 47 digits... Perhaps you wrote the wrong number? 

20050510, 16:28  #3 
"Phil"
Sep 2002
Tracktown, U.S.A.
3·373 Posts 
The exponent should have been written 31, not 13. The composite factor he was working on is listed at www.oddperfect.org as having 110 digits.
Congratulations! 
20050510, 16:51  #4 
May 2003
11000001011_{2} Posts 
R. D. Silverman,
Woops! Yeah, Philmoore got it. 31 is right. :) (Oh, and I hope there are no bad feelings about the religion thread.) Best, Pace Last fiddled with by ZetaFlux on 20050510 at 16:51 
20050511, 00:39  #5  
Mar 2003
New Zealand
13·89 Posts 
Quote:


20050511, 03:49  #6  
"William"
May 2003
New Haven
2^{6}·37 Posts 
Quote:
The SNFS difficulty was 131 digits. The rule of thumb is ECM for 2/9 the size then SNFS. So SNFS would probably have been a better choice than ECM once the 30 digit level was passed. 

20050511, 15:53  #7 
May 2003
7·13·17 Posts 
wblipp,
First, thanks for your comments. Know that if there was an easy way to do SNFS I would probably take a crack at it. From what I've read on this forum, to do SNFS takes quite a bit of effort. Unlike ECM, you can't just plug in the number into a program and let it run. I'm smart enough to probably figure it out one day, but for now I'm just having fun with ECM. :) Second, know that there are an quite a few other unclaimed composite numbers on the site that SNFS people can have fun with, and I just felt like giving ECM a try for a while. Fortunately, I found a factor after only a few days. So, by sheer luck, I didn't have to watch the number of tried curves mount up. geoff, Thanks! Fortunately (and surprisingly) it only took a few curves! 
20050511, 16:10  #8  
"Nancy"
Aug 2002
Alexandria
2,467 Posts 
Quote:
Alex 

20050511, 16:50  #9  
"William"
May 2003
New Haven
2^{6}·37 Posts 
Quote:
I also want to urge people towards the most efficient methods. I haven't figured out how to do that without coming across as a churlish ungrateful troll. Maybe when the work situation calms down a bit I can put together some web pages of guidelines for which method and how to set it up. For now, thanks for the factors and I'm glad you are having fun. 

20050511, 17:13  #10 
May 2003
7×13×17 Posts 
I didn't realize that some of the numbers were better suited to ECM. Wblipp, go ahead and dereserve the C112 for me, and instead I'll work on the C135 (which looks to be the least fitted to SNFS).
Hope that cheers everyone up! :D 
20050511, 17:26  #11 
"Nancy"
Aug 2002
Alexandria
2,467 Posts 
Yep, at difficulty 200, 547^731 c135 is a worthwhile target for ECM. By the 2/9 rule of thumb, ECM to 45 digits would suffice to justify switching to SNFS, but as NFS sievers are in notoriously short supply, going a little further and running a couple of curves at B1=44M as well wouldn't hurt...
Good luck! Alex 
Thread Tools  
Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Modern parameter choice for large 14e/small 15e projects  VBCurtis  Factoring  29  20160212 20:45 
PFGW can't find a small factor.  Arkadiusz  Software  7  20130218 12:43 
newbie question  finding small factors of very large numbers  NeoGen  Math  7  20070313 00:04 
Problems with Large FFT but not Small FFT's?  RichTJ99  Hardware  2  20060208 23:38 
Number with small factor: Further factorization?  Mystwalker  GMPECM  3  20050502 08:31 