A207249 Number of n X 3 0..1 arrays avoiding 0 0 1 and 1 0 1 horizontally and 0 1 0 and 1 0 1 vertically.

6, 36, 102, 370, 1232, 4238, 14406, 49164, 167530, 571202, 1947168, 6638170, 22629802, 77146700, 262997994, 896578158, 3056494736, 10419796218, 35521783770, 121096145300, 412824884294, 1407347734502, 4797742864320

Offset: 1

Author

R. H. Hardin, Feb 16 2012

Keywords

• nonn

Comments

Column 3 of A207254.

Examples

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

Links

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

Crossrefs

Cf. A207254.

Formula

Empirical: a(n) = 2*a(n-1) + 4*a(n-2) + 7*a(n-4) + 8*a(n-5) - a(n-8).

Empirical g.f.: 2*x*(3 + 12*x + 3*x^2 + 11*x^3 + 21*x^4 - 3*x^5 - 3*x^7) / (1 - 2*x - 4*x^2 - 7*x^4 - 8*x^5 + x^8). - Colin Barker, Feb 20 2018