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 16 2019: (Start)
G.f.: 12*x*(1 + 2*x) / (1 - 6*x)^2.
a(n) = 2^(n+1) * 3^(n-1) * (4*n-1).
(End)
EXAMPLE
Some solutions for n=4:
..2..1..1. .1..0..1. .2..2..2. .0..1..0. .0..0..0. .1..0..2. .0..0..0
..0..0..0. .0..2..2. .1..1..0. .2..1..0. .0..0..1. .0..1..0. .1..2..1
..0..0..0. .1..2..1. .2..1..2. .1..0..1. .1..0..2. .0..1..2. .1..0..1
..0..0..0. .2..2..2. .2..2..2. .1..0..1. .0..1..0. .2..1..0. .1..0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 15 2016
STATUS
approved