A266027 Number of n X 2 integer arrays with each element equal to the number of horizontal and antidiagonal neighbors less than itself.

3, 11, 55, 263, 1248, 5959, 28399, 135383, 645407, 3076736, 14667339, 69921635, 333328023, 1589030151, 7575170720, 36112097743, 172152371303, 820678962999, 3912313001599, 18650646247168, 88910730122387, 423852226145531

Offset

1,1

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 3*a(n-1) + 7*a(n-2) + 7*a(n-3) - a(n-4).

Empirical g.f.: x*(3 + 2*x + x^2) / (1 - 3*x - 7*x^2 - 7*x^3 + x^4). - Colin Barker, Jan 09 2019

Example

Some solutions for n=4:
..0..2....0..0....0..1....0..0....0..0....1..0....1..0....1..0....1..0....0..0
..0..2....1..1....2..0....0..0....0..2....0..2....2..0....0..0....1..1....0..2
..1..0....0..2....0..2....0..1....0..0....1..0....1..1....0..1....0..1....1..0
..2..0....0..1....0..0....1..0....2..0....0..1....0..1....2..0....2..0....2..0

Crossrefs

Column 2 of A266033.

Sequence in context: A095707 A259105 A242952 * A306177 A377965 A094259

Adjacent sequences: A266024 A266025 A266026 * A266028 A266029 A266030

Keyword

nonn

Author

R. H. Hardin, Dec 20 2015

Status

approved