Pi Cubed is a visual math application intentionally designed for a touch-based interface. Unlike the usual calculators, Pi Cubed has rich features especially the natural display and wide range of operations and formulas that will let you love it. You can also save your own formulas for future use. A diverse range of mathematical operations are supported, including logarithms, trigonometric functions, arbitrary roots, exponents, and factorials.
I personally use and like this useful application. I am able to save and export my own formulas and all are always with me wherever I go. This is a must-have application.