I want to simplify certain expressions involving integer powers. The expressions are more or less of the form of
Applying PowerExpand to this does not do anything. However,
does simplify to
(-1)^-n. I have tried various other methods of simplification (and adding assumptions) to reproduce the "c" simplification, but I've failed. How can I perform this simplification (and am I missing something on why PowerExpand does not want to do this)?