Mathematical expression for mean of sum of pairs

I can think of at least two representations of the "mean of sum of pairs" in LaTeX code.

documentclass{article}
usepackage{mathtools} % for "smashoperator" macro
begin{document}
raggedright % optional
The ``mean of sum of pairs'' of $H_{ntimes n}$ may be expressed as either
[
frac{2}{n(n-1)} sum_{i=1}^n sum_{j>i} H_{i,j}
quadtext{or as}quad
(n(n-1)/2)^{-1}smashoperator{sum_{substack{i=1,dots,nj>i}}} H_{i,j},.
]
end{document}

end{document}