A199649 Number of n X 2 0..2 arrays with values 0..2 introduced in row major order and each element equal to no more than two horizontal and vertical neighbors.

2, 14, 113, 953, 8037, 67774, 571530, 4819638, 40643380, 342740340, 2890284724, 24373395288, 205537673480, 1733272476824, 14616461440144, 123258718919184, 1039424750772560, 8765333779162336, 73916920107029408, 623331776719986016

Offset: 1

Author

R. H. Hardin, Nov 08 2011

Keywords

• nonn

Comments

Column 2 of A199655.

Examples

			Some solutions for n=3:
..0..1....0..0....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..0
..0..2....1..1....2..2....0..1....1..2....2..0....0..1....2..2....0..2....1..0
..1..2....2..1....0..0....2..1....1..2....1..2....0..2....0..2....2..0....1..0
		

Links

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

Crossrefs

Cf. A199655.

Formula

Empirical: a(n) = 8*a(n-1) + 4*a(n-2) - 2*a(n-3) - 8*a(n-4) for n>6.

Empirical g.f.: x*(2 - 2*x - 7*x^2 - 3*x^3 + 5*x^4 + 4*x^5) / (1 - 8*x - 4*x^2 + 2*x^3 + 8*x^4). - Colin Barker, Mar 02 2018