Big Number Calculator (Free) for Android
There is no error in calculating powers. It may use logarithms and antilog to achieve this. Author can improve the approximation.
It has an "advanced" tab but it's not actually advanced. There's no factorial function, no ^ function for anything larger than cubed. Don't waste your time.
Simple and effective
by T####:
I give it 18^19 and it answers a very far bad answer. Don't download for now