This app "Math for Fun" is an app that lets you kill time by playing around with numbers and guessing interesting math problems and theorems! It has ads, but it's free, so feel free to try it out!

-- Calculate the Collatz conjecture --
If you divide an even number by 2, if you multiply an odd number by 3 and then add 1, the Collatz conjecture says that any number will become 1 if you repeat this process!

-- Find a Pythagorean triple --
Find a set of three natural numbers (a, b, c) that satisfies a² + b² = c²!

-- Make a magic circle --
Make one that has the same total number for each line, vertically, horizontally, and diagonally!

-- Request --
We would appreciate it if you could write a review of math problems that you think would be interesting to add!