It is possible to do stage one P-1 on 2^2N-1 with Prime95 then continue with stage two on 2^N-1 or 2^N+1 separately with gmp-ecm by using the splitcf program (see

http://www.mersenneforum.org/showpos...7&postcount=13). Here is a (trivial) example of doing P-1 on 2^893+1 using this method (some output snipped):

$

$ cat worktodo.ini

Pminus1=1786,3000,1,0,0

$

$ cat lowm.txt

M( 1786 )C: 3

M( 1786 )C: 283

M( 1786 )C: 1787

M( 1786 )C: 174763

M( 1786 )C: 2351

M( 1786 )C: 4513

M( 1786 )C: 524287

M( 1786 )C: 13264529

M( 1786 )C: 6705767506519

$

$ mprime -d

Mersenne number primality test program version 23.5

P-1 on M1786 with B1=3000, B2=3000

M1786 stage 1 complete. 8682 transforms. Time: 0.032 sec.

Stage 1 GCD complete. Time: 0.002 sec.

$

$ pm1dump m0001786 | splitcf -p | ecm -resume - 3000 16000

GMP-ECM 5.0.3 [powered by GMP 4.1.2] [ECM]

Resuming P-1 residue

Input number is 249060...665097 (258 digits)

Using B1=3000-3000, B2=16000, polynomial Dickson(4)

Step 1 took 0ms

Step 2 took 33ms

********** Factor found in step 2: 165768537521

Found probable prime factor of 12 digits: 165768537521

Composite cofactor 150245...858457 has 247 digits

This might be useful for doing P-1 of the Fermat numbers, stage one could be done just once on F(N)-2 with mprime, then using the same save file in each case, do stage two with gmp-ecm on F(N-1), F(N-2), F(N-3), etc.

E.g. if stage one has been done on 2^262144-1 to B1 and the save file is called m0262144, then run these commands (with appropriate low[mp].txt in the current directory) to do stage two on 2^131072+1, 2^65536+1, and 2^32768+1.

pm1dump m0262144 | splitcf -p | ecm -resume - B1 B2

pm1dump m0262144 | splitcf -m | splitcf -p | ecm -resume - B1 B2

pm1dump m0262144 | splitcf -m | splitcf -m | splitcf -p | ecm -resume - B1 B2