public static int MaxNum (int x, int y, int z)

Now, if you've come up with some novel way to perform some computation on three integers and produce an integer:

- you might be able to patent that procedure.

- you might write some code that performs that procedure, and you would hold a copyright over that specific set of code

- you might, I suppose, name your algorithm 'MaxNum' and declare a trademark over it

But I don't think any of those could prevent someone from writing

public static int MaxNum (int x, int y, int z)

in another codebase.

- your patent protection might limit their ability to make a substantially similar implementation of such a function

- your copyright protection might prevent them from literally copying your implementation word for word

- your trademark protection might prevent them from passing off their implementation of MaxNum as if it were yours

But in no way does this have anything to do with the uncopyrightability of mathematics.