A262327 Number of (n+1) X (3+1) 0..1 arrays with each row and column divisible by 3, read as a binary number with top and left being the most significant bits.

6, 15, 90, 351, 2106, 10935, 65610, 378351, 2270106, 13482855, 80897130, 484142751, 2904856506, 17417978775, 104507872650, 626946793551, 3761680761306, 22569180586695, 135415083520170, 812482365290751, 4874894191744506

Offset: 1

Author

R. H. Hardin, Sep 18 2015

Keywords

• nonn

Examples

			Some solutions for n=4:
..0..0..0..0....0..1..1..0....1..0..0..1....0..0..1..1....1..1..1..1
..0..0..0..0....0..1..1..0....1..1..1..1....0..0..1..1....0..0..0..0
..0..0..0..0....0..0..0..0....0..1..1..0....1..0..0..1....1..1..0..0
..1..0..0..1....1..0..0..1....1..0..0..1....1..1..1..1....0..0..1..1
..1..0..0..1....1..0..0..1....1..0..0..1....0..1..1..0....1..1..0..0
		

Links

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

Crossrefs

Column 3 of A262332.

Formula

Empirical: a(n) = 6*a(n-1) + 9*a(n-2) - 54*a(n-3).

Conjectures from Colin Barker, Dec 31 2018: (Start)

G.f.: 3*x*(2 - 7*x - 18*x^2) / ((1 - 3*x)*(1 + 3*x)*(1 - 6*x)).

a(n) = 3^(n-2)*(14 + 2^(2+n)) / 2 for n even.

a(n) = 3^(n-2)*(28 + 2^(2+n)) / 2 for n odd.

(End)