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 17 2019: (Start)
G.f.: 12*x*(1 - x)*(5 - 9*x) / (1 - 9*x)^2.
a(n) = 16*3^(2*n-3) * (8*n+3) for n>1.
(End)
EXAMPLE
Some solutions for n=4:
..1..0..0..0. .1..0..1..2. .2..1..0..1. .2..1..2..1. .2..1..2..1
..1..0..0..1. .0..0..1..2. .0..0..0..0. .2..1..2..2. .2..1..2..2
..0..1..2..0. .1..0..2..2. .1..2..1..2. .2..2..1..2. .0..0..1..2
..2..1..0..0. .0..1..2..1. .1..0..1..0. .1..0..1..1. .1..2..1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 16 2016
STATUS
approved