A268966 Number of n X 3 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once.

24, 240, 2016, 15552, 114048, 808704, 5598720, 38071296, 255301632, 1693052928, 11125776384, 72559411200, 470184984576, 3030081011712, 19434312695808, 124128835928064, 789910774087680, 5010291195641856, 31686706480545792

Offset

1,1

Links

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

Formula

Empirical: a(n) = 12*a(n-1) - 36*a(n-2).

Conjectures from Colin Barker, Jan 17 2019: (Start)

G.f.: 24*x*(1 - 2*x) / (1 - 6*x)^2.

a(n) = 2^(n+2) * 3^(n-1) * (2*n+1).

(End)

Example

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

Crossrefs

Column 3 of A268971.

Sequence in context: A000919 A353665 A353775 * A014340 A052753 A353358

Adjacent sequences: A268963 A268964 A268965 * A268967 A268968 A268969

Keyword

nonn

Author

R. H. Hardin, Feb 16 2016

Status

approved