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A268900 Number of n X 4 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two exactly once. 1
36, 696, 9720, 118584, 1347192, 14644152, 154472184, 1594323000, 16185567096, 162200044728, 1608569870328, 15816054042936, 154394813276280, 1498006261495224, 14458132831535352, 138907883786523192 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = 18*a(n-1) - 81*a(n-2) for n>3.

Conjectures from Colin Barker, Jan 16 2019: (Start)

G.f.: 12*x*(3 + 4*x + 9*x^2) / (1 - 9*x)^2.

a(n) = 8 * 3^(2*n-3) * (16*n-3) for n>1.

(End)

EXAMPLE

Some solutions for n=4:

..0..0..0..1. .1..0..1..2. .2..0..0..0. .2..1..0..0. .1..0..0..1

..0..1..0..0. .1..2..2..1. .1..0..1..2. .1..0..0..0. .1..0..2..2

..0..1..1..0. .2..1..0..1. .1..0..1..2. .0..1..0..0. .1..2..1..2

..0..0..1..2. .2..1..2..0. .1..2..1..2. .2..1..0..0. .2..2..2..1

CROSSREFS

Column 4 of A268904.

Sequence in context: A053947 A157092 A004419 * A185491 A220758 A054339

Adjacent sequences:  A268897 A268898 A268899 * A268901 A268902 A268903

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 15 2016

STATUS

approved

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Last modified October 1 19:48 EDT 2022. Contains 357172 sequences. (Running on oeis4.)