You said "I believe that z is a function of m and n but have no idea how to find out if I'm right." That is simply asking whether or not this is a function, not to find such a function. To answer that you only need to use the definition of "function": a relation, z, on two variables, x and y, is a fuction if and only if \(\displaystyle z(x_1, y_1)\) always gives the same value. Here, looking over your listing, I see that all of the "x, y" values are different- there are no situation where the same x, y values give different z values.
