I have 128 chairs, and 256 people. How many different combinations of the 256 people can be sitting in the 128 chairs? Order doesn't matter, and obviously the same person can't be sitting in more than one chair at a time (no duplicate values in combinations).
Just to clarify, for example, if person 1 is in chair 1 and person 2 is in chair 2 in a given combination, then person 2 being in chair 1 and person 1 being in chair 2 should only count as 1 combination, since they have already been in the same grouping once. I hope that makes sense!