A230520 Number of n X 2 0..2 arrays x(i,j) with each element horizontally, vertically, diagonally or antidiagonally next to at least one element with value (x(i,j)+1) mod 3, and upper left element zero.

0, 12, 78, 576, 4374, 32832, 246726, 1854576, 13938966, 104766048, 787429350, 5918371920, 44482884534, 334336382784, 2512894952070, 18887089079088, 141956643933270, 1066955774448672, 8019312045515046, 60273693833927184

Offset

1,2

Links

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

Formula

Empirical: a(n) = 6*a(n-1) + 9*a(n-2) + 18*a(n-3).

Empirical g.f.: 6*x^2*(2 + x) / (1 - 6*x - 9*x^2 - 18*x^3). - Colin Barker, Sep 22 2018

Example

Some solutions for n=3:
..0..1....0..2....0..0....0..2....0..2....0..1....0..2....0..0....0..1....0..2
..1..2....1..0....2..1....1..2....1..2....0..2....1..2....1..1....2..0....1..0
..1..1....0..2....1..0....1..0....0..2....2..1....2..0....0..2....2..2....2..0

Crossrefs

Column 2 of A230526.

Sequence in context: A189493 A199492 A200055 * A030116 A200036 A224775

Adjacent sequences: A230517 A230518 A230519 * A230521 A230522 A230523

Keyword

nonn

Author

R. H. Hardin, Oct 22 2013

Status

approved