I'm familiar with the concepts of permutations and combinations, however I can't seem to find a formula for the unique combinations of a repeating series. For example if I wanted to find the unique combinations of 3 different digits (from 1-3), that may repeat, how would I do that. Obviously I could go through the process of writing out all the unique combinations,
111 112 113 122 123 133 223 332 222 333
But what If I had to do this for 100 digits? Is there a formula for this. Thanks!