A185899 1/8 the number of n X 2 0..7 arrays with every element equal to exactly one or two of its horizontal and vertical neighbors.

1, 15, 196, 2765, 38731, 545328, 7675381, 108065699, 1521488668, 21421955457, 301612441375, 4246586949080, 59790307544569, 841824567122343, 11852566615920436, 166879587240301061, 2349600516714827299

Offset: 1

Author

R. H. Hardin, Feb 06 2011

Keywords

• nonn

Comments

Column 2 of A185903.

Examples

			Some solutions for 3 X 2 with a(1,1)=0:
..0..1....0..0....0..6....0..0....0..0....0..0....0..0....0..0....0..0....0..7
..0..1....7..0....0..6....0..6....4..0....2..2....5..2....1..1....4..4....0..7
..1..1....7..7....5..5....6..6....4..0....3..3....5..2....3..3....1..1....7..7
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A185903.

Formula

Empirical: a(n) = 13*a(n-1) + 27*a(n-2) - 147*a(n-3) - 245*a(n-4) - 343*a(n-5).

Empirical g.f.: x*(1 + 2*x - 26*x^2 - 41*x^3 - 56*x^4) / (1 - 13*x - 27*x^2 + 147*x^3 + 245*x^4 + 343*x^5). - Colin Barker, Apr 17 2018