A232956 Number of 2 X n 0..3 arrays with no element x(i,j) adjacent to value 3-x(i,j) horizontally, diagonally or antidiagonally, and top left element zero.

4, 21, 129, 771, 4629, 27771, 166629, 999771, 5998629, 35991771, 215950629, 1295703771, 7774222629, 46645335771, 279872014629, 1679232087771, 10075392526629, 60452355159771, 362714130958629, 2176284785751771

Offset: 1

Author

R. H. Hardin, Dec 02 2013

Keywords

• nonn

Examples

			Some solutions for n=5:
..0..1..0..2..3....0..0..0..0..1....0..0..0..1..0....0..1..1..1..0
..3..2..0..2..2....0..1..1..0..2....0..0..1..1..0....0..0..0..1..0
		

Links

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

Crossrefs

Row 2 of A232955.

Formula

Empirical: a(n) = 5*a(n-1) + 6*a(n-2).

Conjectures from Colin Barker, Oct 06 2018: (Start)

G.f.: x*(4 + x) / ((1 + x)*(1 - 6*x)).

a(n) = (25*6^n - 18) / 42 for n even.

a(n) = (25*6^n + 18) / 42 for n odd.

(End)