Number of weak orderings of (i,j), 1 <= i,j <= n, for which there is a set X = {x_1<...<x_n} of n real numbers with (i,j) < (k,m) if and only if x_i + x_j < x_k + x_m.

A378609

Number of weak orderings of (i,j), 1 <= i,j <= n, for which there is a set X = {x_1<...<x_n} of n real numbers with (i,j) < (k,m) if and only if x_i + x_j < x_k + x_m.