A217268 Number of n X 3 arrays of occupancy after each element moves to some horizontal or vertical neighbor.

2, 64, 1472, 33856, 772800, 17640000, 402494400, 9183772224, 209543184576, 4781079618624, 109088244863424, 2489028863068224, 56791310102324928, 1295787666826276416, 29565538631067860928, 674586660240498844224

Offset

1,1

Comments

Column 3 of A217273.

Links

R. H. Hardin, Table of n, a(n) for n = 1..28

Formula

Empirical: a(n) = 24*a(n-1) - 648*a(n-3) + 729*a(n-4) for n>5.

Empirical g.f.: 2*x*(1 + 8*x - 32*x^2 - 88*x^3 + 135*x^4) / ((1 - 24*x + 27*x^2)*(1 - 27*x^2)). - Colin Barker, Jul 23 2018

Example

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

Crossrefs

Cf. A217273.

Sequence in context: A047707 A223121 A134939 * A122603 A127691 A013822

Adjacent sequences: A217265 A217266 A217267 * A217269 A217270 A217271

Keyword

nonn

Author

R. H. Hardin, Sep 29 2012

Status

approved