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 2007-04-19, 22:35 #1 yqiang   Apr 2007 3 Posts using libecm from python Hello, I am writing a wrapper for ecm using python and pyrex. I have successfully wrapped the ecm_factor method defined in ecm.h but am a bit confused about the factors it sometimes finds. If I call ecm_factor(f, n, B1, NULL), the factor it finds is sometimes equal to n. I thought it was supposed to return you a nontrivial factor. Cheers, Yi
 2007-04-20, 08:31 #2 akruppa     "Nancy" Aug 2002 Alexandria 1001101000112 Posts It depends on the parameters. Bad sigma values can cause the trivial factor N to be found, specifically sigma=0,1,2,3 and 5, afaik. Also, if all prime factors in N are relatively small and your B1 value is high enough, ECM can find all factors simultaneously and hence return N as the factor. Alex
 2007-04-22, 00:14 #3 yqiang   Apr 2007 3 Posts Aha, I see. Thanks for your clear explanation. Yi

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