290950domain: NAppears in sequencesNumber of tree-rooted planar maps with 3 faces and n vertices and no isthmuses.at n=21A006470a(n) = n + (n+1)^2 + (n+2)^3 + (n+3)^4.at n=20A027621Number of arrangements of n indistinguishable balls in n boxes with the maximum number of balls in any box equal to n-4.at n=18A180294