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Old 2016-02-19, 05:17   #1
ixfd64
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Default What's the deal with M4,096?

There are a few computers that keep submitting the factors for M4,096. The funny thing is that the exponent isn't even prime. Anyone know what's going on?
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Old 2016-02-19, 06:19   #2
LaurV
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Quote:
Originally Posted by ixfd64 View Post
There are a few computers that keep submitting the factors for M4,096. The funny thing is that the exponent isn't even prime. Anyone know what's going on?
Fermat testing (that is F12).
Those are all different products (i.e. composite) of known F12 small prime factors. People still do lots of ECM trying to get Mr. Guy's money
(edit: or just to make him a present for the 100th b-day celebration in September, which would be very nice!)

Last fiddled with by LaurV on 2016-02-19 at 06:28
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Old 2016-02-19, 06:32   #3
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Quote:
Originally Posted by LaurV View Post
Fermat testing (that is F12).
Erm, M4096 == F12?
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Old 2016-02-19, 06:54   #4
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M4096 = F11 x F10 x F9 ... So work on M4096 is effectively on F11 (since the others are fully factored)
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Old 2016-02-19, 07:17   #5
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Quote:
Originally Posted by fivemack View Post
M4096 = F11 x F10 x F9 ... So work on M4096 is effectively on F11 (since the others are fully factored)
Huh? I thought F11 is full factored too...

Joking apart (I know that was a typo/brainfart on your side), you are both wrong, reality is that PrimeNet does not keep the "M" or "F" but only the exponent, which is either a power of 2, or a prime. He distinguish which, by that. (for example, see here)

In the "recent work" list, on the exponent column (which is labeled Mn, inadvertently):

"4096" means F12
"1061" means M1061

You can report factors for either of them. Like for "1048576" if you like, and PrimeNet knows is a factor of F20, if you have one...

The OP saw the exponent in the list of reported factors (someone indeed reported a lot of composite factors of F12 in the last days) and he assumed it is "M". It is not. Therefore my reply.

Last fiddled with by LaurV on 2016-02-19 at 07:28 Reason: clarification
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Old 2016-02-19, 07:33   #6
ixfd64
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I figured it was F12, but it's weird that the same computers keep sending in the same factors.
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Old 2016-04-06, 16:28   #7
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Quote:
Originally Posted by ixfd64 View Post
I figured it was F12, but it's weird that the same computers keep sending in the same factors.
Wouldn't this occur if they set up their worktodo file to do ECM on F12 but didn't include the list (or product) of known factors? (Reminds me of the old engineers joke: as a last resort, read the manual.)
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Old 2016-04-06, 17:57   #8
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Quote:
Originally Posted by PBMcL View Post
Wouldn't this occur if they set up their worktodo file to do ECM on F12 but didn't include the list (or product) of known factors? (Reminds me of the old engineers joke: as a last resort, read the manual.)
Exactly
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Old 2016-04-06, 19:10   #9
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Quote:
Originally Posted by PBMcL View Post
Wouldn't this occur if they set up their worktodo file to do ECM on F12 but didn't include the list (or product) of known factors?
A long time ago we made that mistake:

http://www.mersenneforum.org/showthread.php?t=106

It starts at post #10 and is very embarrassing since the "factor" ends in a "5".



So, when we actually found a factor once, we spent several hours making sure it was a real factor before posting because we didn't want to look stupid again.

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