Trial factoring a specific number

[Qubit]

Hello,

In Prime95, is there a way to do trial factoring on a number of my choice?
(Just like it's possible with LL, ECM & P-1.)

[Mini-Geek]

Yes, it is. You can add a line to your worktodo.txt file:

Factor=exponent,how_far_factored,how_far_to_factor_to

E.g.

Factor=43112609,70,72

Will factor 2^43112609-1 from 2^70 to 2^72.

[Qubit]

Error: Use ECM instead of trial factoring for exponent: 1277

Hmm, I wonder what is the reason for that.

[Batalov]

http://mersenne.org/various/math.php

http://mersenne.org/report_ecm/

In short, specifically for 1277, all other methods are already done up to impractical sizes and even ECM will take days per curve, if you actually still force Prime95 to run them (B1=850000000 curves, if you have enough RAM). Also, for low values, this is bordering the Cunningham project where certain individuals already may have run plenty of B1=850000000 curves for p=1277. (The 2- series is now in process of extension from 1201 to 1300.)

[petrw1]

Originally Posted by Qubit

Hmm, I wonder what is the reason for that.

Since V25 of Prime95 TF below 20000M is not allowed...for the reasons Batalov suggested.

See: http://www.mersenneforum.org/showpos...&postcount=972

When it says "last 3 should be done" it means 1277, 1619 and 1753 to 61 bits; not factored.

1753 has since been done. 1277 is in progress....ETA another month.