Alright, I'm having a really hard time figuring this out even though I think it should be pretty basic. My question is:
how many unique ways can you pair up a group 16 people so that each person is in a pair?
Eg. if the question was how could you pair up 4 people (ABCD), the answer is 3. You can have AB/CD, AC/BD or AD/BC. Obviously CD/AB is the same as AB/CD so that "different" combination doesn't count. Brute force becomes pretty well impossible for 6 people or more though and I can't seem to google any formula which helps me out.