Need formula to calculate # of unique combinations as n & m vary

Can anyone give me a formula to solve the following kind of problem?

Take n different colors of sand.

Using a minimum quantity m (i.e. 1%) create all the possible % combinations of the colors. {0, 0, 0, .... 100}, {100, 0, 0, 0, ... 0}, {0, 1, 0, 0, ...99}, etc.

I need a formula to calculate how many different unique combinations I would get as n and m vary.

At first I thought I could do this with

n^(m-1)

but I'm not so certain now.

Thx