Some LUA challanges that I did that took longer than it should have.
A function that calculates the volume of the mentioned number/s.
A simple function that finds the Factoiral of the mentioned number.
Another simple function that checks if a number n is divisible by two numbers x AND y.
The longest out of all these, check out the challange for yourself here: https://rosettacode.org/wiki/100_doors.