mersenneforum.org Looking for factorization program
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 2006-08-18, 01:49 #1 Unregistered   3×37 Posts Looking for factorization program Hi, I can't find a factorization/prime confirmation program that does factors larger than about 50-70 digits. I tried alpertron's ECM applet, and know absolutely nothing about programming languages used. Can anyone help? Thanks.
 2006-08-18, 06:56 #2 akruppa     "Nancy" Aug 2002 Alexandria 246710 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
 2006-08-18, 14:50 #3 alpertron     Aug 2002 Buenos Aires, Argentina 52816 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 2006-08-18 at 14:52
 2006-08-18, 18:32 #4 Unregistered   2×3×52×43 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.
 2006-08-18, 18:33 #5 Unregistered   7×263 Posts PS, And yes, both factors are the same size Thanks.
 2006-08-18, 18:44 #6 alpertron     Aug 2002 Buenos Aires, Argentina 23×3×5×11 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?
2006-08-18, 18:45   #7
jasonp
Tribal Bullet

Oct 2004

DC816 Posts

Quote:
 Originally Posted by Unregistered PS, And yes, both factors are the same size Thanks.
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

 2006-08-18, 19:56 #8 Unregistered   22×1,867 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 143-digit one, and can't factorize it. Thanks, JasonP, I'll check that out.
2006-08-18, 20:02   #9
Uncwilly
6809 > 6502

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Aug 2003
101×103 Posts

8,423 Posts

Quote:
 Originally Posted by Unregistered 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 143-digit one, and can't factorize it.
Sounds like a cryptography issue....

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