A268792 Number of n X 2 0..2 arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two exactly once.

3, 22, 78, 234, 652, 1714, 4360, 10820, 26366, 63346, 150482, 354196, 827310, 1919884, 4430664, 10175910, 23272918, 53029498, 120435100, 272714858, 615904208, 1387638220, 3119557838, 6999162874, 15675003042, 35046218020

Offset

1,1

Links

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

Formula

Empirical: a(n) = 2*a(n-1) + 3*a(n-2) - 2*a(n-3) - 6*a(n-4) - 4*a(n-5) - a(n-6) for n>7.

Empirical g.f.: x*(3 + 16*x + 25*x^2 + 18*x^3 + 12*x^4 + 8*x^5 + 3*x^6) / (1 - x - 2*x^2 - x^3)^2. - Colin Barker, Jan 15 2019

Example

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

Crossrefs

Column 2 of A268798.

Sequence in context: A178492 A005288 A143166 * A055550 A075204 A106150

Adjacent sequences: A268789 A268790 A268791 * A268793 A268794 A268795

Keyword

nonn

Author

R. H. Hardin, Feb 13 2016

Status

approved