A207769 Number of n X 3 0..1 arrays avoiding 0 0 0 and 1 1 1 horizontally and 0 0 1 and 0 1 0 vertically.

6, 36, 84, 192, 450, 972, 2040, 4278, 8910, 18462, 38214, 79044, 163386, 337638, 697668, 1441488, 2978208, 6153084, 12712374, 26263824, 54261060, 112103226, 231604842, 478494570, 988567506, 2042375592, 4219537710, 8717543538

Offset: 1

Author

R. H. Hardin, Feb 20 2012

Keywords

• nonn

Comments

Column 3 of A207774.

Examples

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

Links

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

Crossrefs

Cf. A207774.

Formula

Empirical: a(n) = 3*a(n-1) - 2*a(n-2) + a(n-3) - 2*a(n-4) + a(n-6) for n>7.

Empirical g.f.: 6*x*(1 + 3*x - 2*x^2 + x^3 + 3*x^4 - x^5 - x^6) / ((1 - x)^2*(1 - x - x^2 - 2*x^3 - x^4)). - Colin Barker, Jun 25 2018