Partial integer factorization?

[Jeroen Demeyer <jdemeyer@cage.ugent.be>]

Hello,

Is there way in PARI/GP to factor an integer partially, and possibly 
keeping hard-to-factor composites?  I had a look a factorint(n, 9) which 
works, but does only really trivial factorizations.  This does not 
factor 165293388715327472724574326428939 for instance, which takes less 
than 100ms with MPQS.

I would like to say ``try ECM to some extent, possibly MPQS if the 
number is not too big''.  I realize this could be a difficult question.


Jeroen