Mathematics

Problem

For a set with

n

(n\ge 2)

elements, which of the following expressions equals the number of symmetric but not reflexive relations on the set? a)

2^{\frac{n(n-1)}{2}+n}\; -\; 1

2^{\frac{n(n-1)}{2}+n}

2^{\frac{n(n-1)}{2}+n}\; -\; 2^{\frac{n(n-1)}{2}}

2^{\frac{n(n-1)}{2}+n}\; -\; 2^{n}