A207840 Number of n X 3 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 0 and 1 1 1 vertically.

6, 36, 72, 240, 704, 2080, 6216, 18496, 55000, 163760, 487296, 1450192, 4315896, 12844160, 38224536, 113757504, 338545344, 1007520656, 2998410360, 8923354336, 26556156776, 79031879392, 235201123584, 699965244000, 2083116504872

Offset: 1

Author

R. H. Hardin, Feb 21 2012

Keywords

• nonn

Comments

Column 3 of A207845.

Examples

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

Links

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

Crossrefs

Cf. A207845.

Formula

Empirical: a(n) = a(n-1) + 4*a(n-2) + 5*a(n-3) + 2*a(n-4) - a(n-5) + a(n-6) for n>8.

Empirical g.f.: 2*x*(3 + 15*x + 6*x^2 - 3*x^3 - 8*x^4 - 5*x^5 + 3*x^6 - 2*x^7) / (1 - x - 4*x^2 - 5*x^3 - 2*x^4 + x^5 - x^6). - Colin Barker, Feb 21 2018