Quote:
Originally Posted by CRGreathouse
The problem is hard and in general cannot be done symbolically.
For that one you'll need a special function like Lambert's W, or numerical techniques. I think it's exp(W(log N)). W(x) is about log x  log log x, so this is roughly exp(log log N  log log log N) = log N / log log N, where log is the natural log.

if he didn't want work I'd say use PARI's ispower() with a loop through base values.