A268803 Number of n X 2 0..2 arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two not more than once.

9, 34, 104, 290, 772, 1972, 4914, 12010, 28922, 68836, 162274, 379524, 881712, 2036734, 4681646, 10714994, 24430816, 55516546, 125777028, 284188780, 640549034, 1440572818, 3233256010, 7243375068, 16199546178, 36172883716

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*(9 + 16*x + 9*x^2 - 2*x^3 + 2*x^4 + 6*x^5 + 3*x^6) / (1 - x - 2*x^2 - x^3)^2. - Colin Barker, Jan 15 2019

Example

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

Crossrefs

Column 2 of A268809.

Sequence in context: A000441 A067989 A002881 * A250652 A005344 A250763

Adjacent sequences: A268800 A268801 A268802 * A268804 A268805 A268806

Keyword

nonn

Author

R. H. Hardin, Feb 13 2016

Status

approved