Thread: P-1 stage 2 with GMP-ECM 5 ? View Single Post
 2004-04-27, 16:06 #8 geoff     Mar 2003 New Zealand 13·89 Posts 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