682920domain: NAppears in sequencesa(0)=1, a(n) = sigma_3(3n).at n=29A092341Triangular array read by rows. T(n,k) is the number of labeled rooted trees of height at most 2 with exactly k leaves at a distance 1 from the root, n>=1, 0<=k<=n-1.at n=47A220233a(n) = (n - 1)*(n^3 + 1) = n^4 - n^3 + n - 1, for n >= 1.at n=28A242604