Quote:
Originally Posted by axn
Obviously, this doesn't involve factoring the composite factor's k -- that part is very much useless.
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It's not entirely useless.
Every factor of a Mersenne number is of the form q = 2kp + 1, so q−1 = 2kp. Here "q" is the "P" of the P−1 factorization method, so displaying the factorization of k tells you at a glance how powersmooth q−1 is.
You can see at a glance (after the fact, of course) what the smallest bounds of B1 and B2 would have been for finding that factor with the P−1 method. So you could often distinguish at a glance how likely it was that the factor was found with P−1, as opposed to ECM or TF.