A263366 Number of (n+1) X (1+1) 0..2 arrays with each row and column divisible by 7, read as a base-3 number with top and left being the most significant digits.

1, 1, 2, 5, 10, 19, 37, 73, 146, 293, 586, 1171, 2341, 4681, 9362, 18725, 37450, 74899, 149797, 299593, 599186, 1198373, 2396746, 4793491, 9586981, 19173961, 38347922, 76695845, 153391690, 306783379, 613566757, 1227133513, 2454267026, 4908534053

Offset: 1

Author

R. H. Hardin, Oct 16 2015

Keywords

• nonn

Examples

			All solutions for n=4:
..2..1....0..0....2..1....0..0....2..1
..0..0....2..1....0..0....0..0....2..1
..2..1....0..0....0..0....0..0....0..0
..0..0....0..0....2..1....0..0....2..1
..2..1....2..1....0..0....0..0....2..1
		

Links

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

Crossrefs

Column 1 of A263373.

Formula

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

Empirical g.f.: x*(1 - 2*x + 2*x^2 - x^3 + x^4 - 2*x^5) / ((1 - x)*(1 - 2*x)*(1 - x + x^2)*(1 + x + x^2)). - Colin Barker, Jan 01 2019