OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 2*a(n-2) - a(n-4) for n>6.
Empirical g.f.: x*(2 + 7*x + 3*x^2 - 6*x^3 - 2*x^4 + x^5) / (1 - x - 2*x^2 + x^4). - Colin Barker, Feb 04 2019
EXAMPLE
Some solutions for n=4:
..0..1. .0..0. .0..0. .0..0. .0..1. .0..1. .0..1. .0..0. .0..0. .0..0
..1..1. .1..1. .1..1. .1..1. .1..1. .1..1. .1..1. .0..1. .0..1. .0..1
..2..2. .1..2. .1..2. .2..2. .2..2. .1..2. .1..2. .1..2. .1..2. .1..1
..0..0. .2..2. .2..0. .2..0. .2..0. .2..0. .0..0. .2..2. .1..2. .1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jul 30 2016
STATUS
approved