A185405 1/7 the number of n X 2 0..6 arrays with every element equal to exactly one or two of its horizontal and vertical neighbors.

1, 13, 150, 1848, 22656, 278832, 3430776, 42221928, 519611520, 6394769688, 78699293256, 968538893952, 11919644165496, 146693048343528, 1805326578739200, 22217849450044248, 273431322619829256

Offset: 1

Author

R. H. Hardin, Jan 26 2011

Keywords

• nonn

Comments

Column 2 of A185409.

Examples

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

Links

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

Crossrefs

Cf. A185409.

Formula

Empirical: a(n) = 11*a(n-1) + 23*a(n-2) - 72*a(n-3) - 144*a(n-4) - 216*a(n-5).

Empirical g.f.: x*(1 + 2*x - 16*x^2 - 29*x^3 - 42*x^4) / (1 - 11*x - 23*x^2 + 72*x^3 + 144*x^4 + 216*x^5). - Colin Barker, Apr 15 2018