OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + 3*a(n-3).
Empirical g.f.: x*(4 + 4*x + 3*x^2) / (1 - 3*x - 3*x^2 - 3*x^3). - Colin Barker, Feb 20 2019
EXAMPLE
Some solutions for n=4:
..0..1. .0..1. .1..0. .1..1. .1..1. .1..0. .1..0. .0..0. .1..1. .1..0
..0..0. .1..0. .0..1. .1..1. .0..1. .1..0. .1..1. .1..1. .1..1. .1..1
..0..1. .0..1. .0..0. .1..0. .0..1. .0..0. .1..1. .0..0. .0..0. .0..1
..0..0. .0..1. .1..0. .1..0. .0..1. .1..0. .1..0. .0..0. .1..1. .0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 11 2017
STATUS
approved