OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) + 6*a(n-2) + 3*a(n-3) - 6*a(n-4).
Empirical g.f.: x^2*(9 - 2*x - 2*x^2) / (1 - 6*x - 6*x^2 - 3*x^3 + 6*x^4). - Colin Barker, Feb 06 2019
EXAMPLE
Some solutions for n=4:
..0..0. .0..1. .0..1. .0..2. .0..1. .0..1. .0..1. .0..1. .0..2. .0..1
..1..2. .2..0. .2..1. .1..1. .2..0. .2..1. .2..1. .2..0. .1..2. .1..2
..2..1. .2..0. .2..0. .2..1. .1..1. .2..0. .1..0. .1..0. .1..2. .0..1
..0..0. .1..0. .1..2. .0..0. .0..0. .1..0. .2..0. .1..2. .0..2. .0..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 08 2016
STATUS
approved