--- In ggnfs@yahoogroups.com, "chris2be8" <chris2be8@...> wrote:
> When factoring something like a^3k-1 I first algebraically reduce it to
(a^2k+a^k+1)(a^k-1). To crack the first part I need to convert it into a degree
4 or 6 poly, where is the crossover point where I get better results from degree
6?

Crossover from degree 4 to 6 (when 5 is not possible) is about difficulty
145-150 digits. Note: One sieving side, algebraic or rational, will be much
faster than the other, and this choice is going to be opposite for 4 vs 6. In
the grey area around 150 digits, some trial sieving will help to decide. Also,
using uneven bounds (r/alim, lpbr/a) should be tried -- with the right choice,
these can save some sieving time.