A203357 Number of n X 3 binary arrays with every 1 immediately preceded by 0 to the left or above.

3, 20, 102, 565, 3042, 16538, 89610, 486103, 2635899, 14295131, 77522409, 420410296, 2279906481, 12364072580, 67051079697, 363621959233, 1971943176024, 10693963589630, 57993991716273, 314504819239756, 1705578083028348

Offset: 1

Author

R. H. Hardin, Dec 31 2011

Keywords

• nonn

Comments

Column 3 of A203362.

Examples

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

Links

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

Crossrefs

Cf. A203362.

Formula

Empirical: a(n) = 3*a(n-1) +12*a(n-2) +6*a(n-3) +a(n-4).

Empirical g.f.: x*(3 + 11*x + 6*x^2 + x^3) / (1 - 3*x - 12*x^2 - 6*x^3 - x^4). - Colin Barker, Jun 04 2018