12927600domain: NAppears in sequencesNumbers k for which k = sigma(sigma(x)) = sigma(sigma(y)) for some x and y such that k = x + y.at n=13A229953Table read by ascending antidiagonals: T(n, k) is the maximum number of quasi k-gons that are not k-gons in a finite projective plane of order n, with k >= 3.at n=12A342307