Thanks Dima, you taught me something new today.
Guillermo
On Sun, 29 Jan 2023 at 20:50, Dima Pasechnik <dimp...@gmail.com> wrote:
> On Sun, Jan 29, 2023 at 3:04 PM G. M.-S. <lists....@gmail.com> wrote:
> >
> > For me, with SageMath version 9.8.beta7
> > sage: ecm.factor(71281426948143699070565)
> > does not return quickly either.
> > Indeed, running
> > sage: ecm.interact()
> > seems to show a strange behaviour for 71281426948143699070565 when
> factoring the factors found.
> > As this is probabilistic and the output changes every time, I do not
> copy it here.
>
> Basically, the default B1 value is too large in this case.
>
> sage: ecm.factor(71281426948143699070565,B1=200) # almost instant
> [5, 53, 337, 1873, 2833, 7507, 20037791]
> sage: ecm.factor(71281426948143699070565,B1=2000) # takes looong time
>
> the docs say:
>
> * "B1" -- initial lower bound, defaults to 2000 (15 digit factors).
> Used if "factor_digits" is not specified.
>
> > Guillermo
> >
> > On Sun, 29 Jan 2023 at 15:41, Bill Witzke <bwitzk...@gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> I have a hard time factoring the number 71281426948143699070565 using
> ecm.factor(). No result is given after a few minutes runtime. Though,
> plain factor() happily factors the number. Factoring smaller or larger
> numbers work fine with ecm.factor(), too. Just the single given number
> seems to be problematic.
> >>
> >> Am I doing something wrong? Can someone confirm?
> >>
> >> system:
> >> Ubuntu 22.04
> >> sagemath 9.5-4 (via apt)
> >> Intel Pentium N5000
> >> (SageMath and Python beginner)
> >>
> >> example code factoring numbers in the range [71281426948143699070565 -
> L, 71281426948143699070565 + L]:
> >>
> >> # Odd number.
> >> n = 71281426948143699070565
> >> # Limit.
> >> L = 2
> >> # Iterate over interval [-L, L].
> >> for i in range(-L, L + 1):
> >> m = n + i
> >> print("%d => %s" % (m, ecm.factor(m)))
>
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