390656domain: NAppears in sequencesa(n) = Sum_{k=0..7} binomial(n,k).at n=23A008860Number of 1-punctured staircase polygons (by perimeter) with a hole of perimeter 4.at n=15A055022a(n) = Sum_{k=0..n} binomial(3*n+2,k).at n=7A387007