A317759 Number of nX2 0..1 arrays with every element unequal to 0, 1 or 2 horizontally, vertically or antidiagonally adjacent elements, with upper left element zero.

2, 6, 10, 20, 42, 89, 190, 407, 873, 1874, 4024, 8642, 18561, 39866, 85627, 183917, 395034, 848492, 1822474, 3914489, 8407926, 18059375, 38789713, 83316386, 178955184, 384377666, 825604417, 1773314930, 3808901427, 8181135701

Offset: 1

Author

R. H. Hardin, Aug 06 2018

Keywords

• nonn

Comments

Column 2 of A317764.

Examples

			Some solutions for n=5
..0..0. .0..1. .0..1. .0..0. .0..0. .0..0. .0..0. .0..0. .0..1. .0..0
..1..1. .1..1. .1..1. .1..1. .1..1. .0..0. .0..1. .0..1. .1..1. .0..0
..1..1. .0..0. .1..1. .1..0. .1..1. .0..0. .1..1. .1..1. .0..0. .1..1
..0..0. .0..0. .1..1. .0..0. .1..1. .0..1. .0..0. .1..1. .0..1. .1..1
..0..0. .1..1. .1..0. .0..1. .0..0. .1..1. .0..1. .1..0. .1..1. .0..0
		

Links

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

Crossrefs

Cf. A317764.

Formula

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