OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 4*a(n-2) + a(n-3) for n>4.
Empirical g.f.: x*(1 - x)*(1 + x)*(2 + x) / (1 - 4*x - 4*x^2 - x^3). - Colin Barker, Feb 15 2019
EXAMPLE
Some solutions for n=4:
..0..1. .0..1. .0..1. .0..1. .0..1. .0..1. .0..0. .0..0. .0..1. .0..1
..0..2. .2..0. .1..2. .2..1. .2..2. .2..2. .1..1. .1..2. .2..2. .2..0
..1..0. .1..2. .0..2. .0..2. .1..0. .1..0. .2..2. .2..0. .1..0. .0..1
..0..1. .0..0. .1..1. .1..0. .1..0. .2..2. .0..1. .1..1. .0..2. .2..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 11 2017
STATUS
approved