A269030 Number of n X 3 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two exactly once.

12, 48, 348, 2136, 12228, 67104, 357756, 1867560, 9593844, 48665904, 244357740, 1216672824, 6015296484, 29561944128, 144531868764, 703461546312, 3410368965588, 16475694411600, 79347347565132, 381071870841432

Offset

1,1

Links

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

Formula

Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4) for n>5.

Empirical g.f.: 12*x*(1 - 6*x + 18*x^2 - 16*x^3 + 4*x^4) / (1 - 5*x + 2*x^2)^2. - Colin Barker, Jan 18 2019

Example

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

Crossrefs

Column 3 of A269035.

Sequence in context: A052601 A003498 A326743 * A222359 A002899 A222966

Adjacent sequences: A269027 A269028 A269029 * A269031 A269032 A269033

Keyword

nonn

Author

R. H. Hardin, Feb 18 2016

Status

approved