We like how in GMP-ECM you can tell it to use a formula, instead of having to use the decimal expansion like it used to be.

What we think would be cool is if the program would show the first 3 digits and then the last 3 digits of the number, or some arbitrary number of digits, to verify that the formula is typed in properly. (In our case we use bc to make sure the number is right but we have no idea if what GMP-ECM is using is right, other than the number of digits listed in the output.)

For example, one of the lists we have has the first few digits printed, so you are pretty sure you have the right thing typed in if those digits match. Since we sometimes have to divide out 3 or more huge factors the chance of us typing the number wrong is pretty good, since we can barely type to begin with.

So maybe the output would look like this:

Code:

GMP-ECM 6.1.1 [powered by GMP 4.2.1] [ECM]
Input number is (12^229-1)/841357 (242 digits) (161...843)
Using B1=850000000, B2=15892628251516, polynomial Dickson(30), sigma=2176429102

Dumb idea?