Actually, n! / (2! * (n-2)!) comes out exactly at n * (n-1)/2. It's just one form of the general formula for combinations. However, multiplying the possible si

Actually, n! / (2! * (n-2)!) comes out exactly at n * (n-1)/2. It's just one form of the general formula for combinations. However, multiplying the possible situations is, of course, wrong. A case of a wrong explanation of the final result I'd imagine (permutations instead of combinations),