M2 not prime?

James Heinrich · 2005-02-28, 19:06

I'm not sure if this is a math or software question, but according to Prime95 M2 is not prime

You can't do Advanced | Test for M < 5, but you can throw this into worktodo.ini:

Quote:

AdvancedTest=2

and it'll come back with something like this:

Quote:

M2 is not prime. Res64: 5555555555555555. WZ1: AAAEAAAF,1,00000000

Is that a bug or am I wrong that M2 is prime? M3 onwards works fine:

Quote:

M3 is prime! WZ1: 00060006,00000000

ewmayer · 2005-02-28, 19:11

M2 = 2^2 - 1, more commonly known as the number 3. I'll let you figure out whether it's prime or not.

(Hint: most programs like Prime95 are heavily optimized for *large* numbers.)

James Heinrich · 2005-02-28, 19:16

Yes, exactly.
I'm sure we can agree that Prime95 isn't required to determine if 3 (M2) or 7 (M3) is prime, but it shouldn't say that M2 is not prime when it is...

Bundu · 2005-02-28, 20:31

I'm sad because I took the time to look at this......lol

ewmayer · 2005-02-28, 22:57

Quote:

Originally Posted by James Heinrich

I'm sure we can agree that Prime95 isn't required to determine if 3 (M2) or 7 (M3) is prime, but it shouldn't say that M2 is not prime when it is...

True. From your description, it sounds like George simply forgot to invoke a minimum-exponent-size check when the Advanced menu is accessed from the worktodo.ini file (as opposed to the pulldown menu on the GUI.)

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2005-02-28, 19:11	#2
ewmayer ∂²ω=0 Sep 2002 República de California 19·613 Posts	M2 = 2^2 - 1, more commonly known as the number 3. I'll let you figure out whether it's prime or not. (Hint: most programs like Prime95 are heavily optimized for large numbers.)

2005-02-28, 19:16	#3
James Heinrich "James Heinrich" May 2004 ex-Northern Ontario 23×149 Posts	Yes, exactly. I'm sure we can agree that Prime95 isn't required to determine if 3 (M2) or 7 (M3) is prime, but it shouldn't say that M2 is not prime when it is...

2005-02-28, 20:31	#4
Bundu Jul 2004 Mid Calder, Scotland 185₁₀ Posts	I'm sad because I took the time to look at this......lol