ECMNET Frequently Asked Questions

Q: How does one recognize a new factor was found?
A: Some lines as follows appear in the output file:

Q: How to use ecm.exe as batch file under Windows?
A: See the ecmloop.bat file from Warut Roonguthai

Q: The value of B1 in the output file cunningham.out is always 0. What happens?
A: Please check your command looks like "ecm 3000000". Check "ecm -v" for more information about the command line.

Q: What do the lines "recognized factor of 2^631+1, using special base-2 division" mean?
A: They mean the program has detected the input number if a divisor of a power of two plus or minus one, and is using a faster division. This does not mean a new factor was found.

Q: Can I change the recommended value B1=3000000?
A: Yes: a smaller (resp. greater) value will take less time per curve and will have less (resp. more) chance of finding a factor. However this value of B1=3000000 is optimal for the expected size of new factors (about 40 digits). See the table of optimal B1 wrt factor size.

Q: Do I loose all results if I restart the program?
A: No, you only loose the computations done in the current curve.