20060818, 01:49  #1 
3×37 Posts 
Looking for factorization program
Hi,
I can't find a factorization/prime confirmation program that does factors larger than about 5070 digits. I tried alpertron's ECM applet, and know absolutely nothing about programming languages used. Can anyone help? Thanks. 
20060818, 06:56  #2 
"Nancy"
Aug 2002
Alexandria
2467_{10} Posts 
ECM is good if the prime factor is not too large, say not much above 50 digits, but large input numbers are not much of a problem.
NFS is good ig the composite input number is not too large, say not much above 150 digits, regardless of how large the smallest remaining prime factor is. So in order to give proper advice, we'd need to how large the composite number will be and how large the prime factors can be expected to be. Alex 
20060818, 14:50  #3 
Aug 2002
Buenos Aires, Argentina
528_{16} Posts 
Is the composite number 155 digits long with two prime factors of the same size (about 78 digits)?
Last fiddled with by alpertron on 20060818 at 14:52 
20060818, 18:32  #4 
2×3×5^{2}×43 Posts 
Right now I'm working on 143 digit numbers, but will be going higher later
Thanks for your advice! PS, Alpertron, Your site has still been extremely helpful to me! Thanks. 
20060818, 18:33  #5 
7×263 Posts 
PS,
And yes, both factors are the same size Thanks. 
20060818, 18:44  #6 
Aug 2002
Buenos Aires, Argentina
2^{3}×3×5×11 Posts 
Thanks for your comments.
How do you know that the both prime factors of your number have the same size if you haven't factored it? 
20060818, 18:45  #7 
Tribal Bullet
Oct 2004
DC8_{16} Posts 
GGNFS is pretty much the only choice available that has a realistic shot at factoring numbers that big. The good news is that it has managed to solve even larger problems than that. The bad news is that even with a nice perl script, it takes some getting used to. I'd recommend downloading one of the binary distributions and trying it out on some small problems (maybe 100 digits) to get the hang of it before embarking on a major effort like a C143. Depending on the resources you have available, a job that big can take weeks.
jasonp 
20060818, 19:56  #8 
2^{2}×1,867 Posts 
Thanks, all
To alpertron, I know the factors because I am looking for primes via a method that uses primes multiplied togeather. Eventually I got to the 143digit one, and can't factorize it. Thanks, JasonP, I'll check that out. 
20060818, 20:02  #9 
6809 > 6502
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Aug 2003
101×103 Posts
8,423 Posts 

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