A268623 Number of n X 3 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two no more than once.

24, 174, 1086, 6300, 34890, 187224, 982086, 5063964, 25764066, 129678528, 646978302, 3204131172, 15769455258, 77195600520, 376136512950, 1825265294892, 8825528262738, 42536536932432, 204425809550958, 979908028544244

Offset: 1

Author

R. H. Hardin, Feb 09 2016

Keywords

• nonn

Examples

			Some solutions for n=6:
..0..0..1. .0..0..0. .2..2..1. .1..0..1. .1..2..1. .1..0..1. .1..0..1
..0..1..2. .1..0..0. .0..1..2. .0..0..0. .0..1..2. .0..1..2. .0..0..0
..2..2..2. .0..1..0. .1..0..1. .1..0..0. .0..0..1. .1..0..1. .1..1..0
..1..2..2. .1..2..1. .0..1..0. .0..0..1. .1..0..0. .2..1..0. .0..0..0
..2..1..2. .0..1..0. .1..0..1. .2..1..0. .2..2..1. .2..0..1. .1..0..0
..1..2..2. .0..1..0. .0..1..2. .1..0..1. .1..2..2. .2..1..2. .2..1..0
		

Links

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

Crossrefs

Column 3 of A268628.

Formula

Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4).

Empirical g.f.: 6*x*(4 - 11*x + 7*x^2 + x^3) / (1 - 5*x + 2*x^2)^2. - Colin Barker, Jan 14 2019