CalcWrite 4.0

the author of this app says:

Write on the screen with your stylus to enter math problems into your device.

After you enter a problem, the program calculates the result. If you mess up a digit, you can just write over it. This application also has two powerful features that allow you to recalculate handwritten items and display a mini-spreadsheet that automatically recalculates for you.

The program was recently updated and now has support for brackets, percentages and square roots.