The ECM choice lets you factor Mersenne numbers using the Elliptic Curve Method of factoring.  Select a few exponents and bounds to factor from the http://www.mersenne.org/ecm.htm web pages.

 

 

Note:  You do not reserve exponents to work on, several people can do ECM factoring on the same exponent.  The program uses a random number generator to select elliptic curves to test.  You must email results to me at woltman@alum.mit.edu - PrimeNet does not support ECM factoring.  WARNING:  ECM does not adhere to the memory limits specified in the Options / CPU dialog box.  ECM requires a minimum of 192 times the FFT size.  Thus, ECM factoring of F20 which uses a 64K FFT will use a minimum of 192 * 64K or 12MB of memory.  You can also edit the worktodo.ini file directly.  For example:

 

                ECM=751,3000000,0,100,0,0,0,0

 

The first value is the exponent.  The second value is bound #1.  The third value is bound #2 - leave it as zero.  The fourth value is the number of curves to test.  The fifth value is no longer used.  The sixth value is the specific curve to test - it is only used in debugging.  The seventh value is 0 for 2^N-1 factoring, 1 for 2^N+1 factoring.  The eighth value is no longer used.