What does the little number to the bottom right of a number mean in algebraic expressions?

I am trying to do programming homework and I have to convert an algebraic expression into java speak. This class had no algebra prerequisite and I think it should have because I don’t remember Algebra. If I knew what that little number was called I could look it up and figure it out on my own but I have no clue! Help please! One portion of it is x (0)<———-0 is the little number on the bottom right.