Two features in this app.
First: The Syracuse problem or also called the Collatz conjecture is one of the most famous unsolved problems in mathematics. The conjecture asks whether repeating two simple arithmetic operations will eventually transform every positive integer into 1. Play with integers and check the result. See how small changes gives huge values but still eventually ends up down to 1. Find the number of calculations needed and the biggest value reached doing so.
Second: Find the roots in a quadratic equation.