I have four objects - for the sake of arguments, let say that they are the following letters: A B C D

I need to calculate the number of variations that can be made for these under the following two conditions:

1. No repetition
2. Objects are position agnostic

Taking the above, this means that with a four object sequence, I can have only one sequence that matches the criteria (since order is not considered for being unique):

• ABCD

There are four variations for a three object combination from the four object pool:

• ABC, ABD, ACD, and BCD

There are six variations for a two object combination from the four object pool:

• AB, AC, AD, BC, BD, and CD

And the most simple one, if taken on at a time:

• A, B, C, and D

I swear that this was something covered in school, many, many years ago - and probably forgotten since I didn't think I would use it. :-) I am anticipating that factorials will come into play, but just trying to force an equation is not working.

Any advice would be appreciated.