JEE Advance 2025 Paper 1

Let the set of all relations $R$   on the set $\{a, b, c, d, e, f\}$  , such that $R$   is reflexive and symmetric, and $R$   contains exactly 10 elements, be denoted by $\mathcal{S}$  . Then the number of elements in $\mathcal{S}$   is