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-   -   Typo in reported factor? (https://www.mersenneforum.org/showthread.php?t=15279)

R.D. Silverman 2011-02-19 23:03

Typo in reported factor?
 
Bruce reports finding a factor of 6^391-1 on the ECMNET webpage.

But unless my software is really screwing up, the factor does
not divide. I am guessing that one or more digits are missing?

Batalov 2011-02-19 23:17

Yep, it is 7,359-.
Cofactor c224 is composite.

(It must have divided a number from the list because othewise Paul's form wouldn't accept it. This sudoku puzzle was easy.)

bdodson 2011-02-20 02:20

[QUOTE=Batalov;253066]Yep, it is 7,359-.
Cofactor c224 is composite.

(It must have divided a number from the list because othewise Paul's form wouldn't accept it. This sudoku puzzle was easy.)[/QUOTE]

Yes, sorry; and thanks. Different c27x first five hole. But another
small one; seems likely that there are more to find. Too many new
inputs over the weekend, when many of the labs are closed. Distracted
by exam grading and _three_ new top5000 Proth primes. Plus the wind
knocked out our power for two hours here today.
Regards, Bruce
---

bdodson 2011-02-21 02:14

[QUOTE=Batalov;253066]
(It must have divided a number from the list because othewise Paul's form wouldn't accept it. This sudoku puzzle was easy.)[/QUOTE]

OK, how's about this one?
474942339376967475871960321762614254290810243038880418971061342256529

2nd hole. -bd

Batalov 2011-02-21 02:34

A hole in one. Now, this is not a futile factor. :-)

Congratulations!

bdodson 2011-02-21 14:33

[QUOTE=Batalov;253221]A hole in one. Now, this is not a futile factor. :-)

Congratulations![/QUOTE]

Here's the group order:

[code]
Magma V2.16-4 Mon Feb 21 2011 09:16:48 on altair1 [Seed =3370645033]

[ <2, 2>, <3, 2>, <7, 2>, <11, 2>, <53, 1>, <353, 1>, <467, 1>, <779591,1>,
<1057367, 1>, <15751453, 1>, <40771103, 1>, <43303219, 1>, <356236847,1>,
<31186368729239, 1> ] [/code]

So that's p = 356236847 < 400M = B1 for the step1 prime,
q = 31186368729239 > 1.59e13 = B2 for the step2. Ooops. If it matters,
this ran with k = 20. Sounds like this really used some GMP-ECM features;
and I was more than just lucky with the parameters!

Bruce (This is the new p69 by ecm, from 2,1822L C197.)


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