OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 16*a(n-1) - 72*a(n-2) + 64*a(n-3) - 16*a(n-4).
Empirical g.f.: 4*x^2*(1 - 6*x) / (1 - 8*x + 4*x^2)^2. - Colin Barker, Feb 11 2019
EXAMPLE
Some solutions for n=4:
..0..1. .0..1. .0..1. .0..1. .0..0. .0..0. .0..0. .0..1. .0..1. .0..1
..2..0. .2..0. .2..1. .2..0. .1..0. .1..0. .1..0. .0..2. .2..1. .0..2
..0..2. .2..2. .1..0. .2..2. .0..2. .1..0. .1..0. .2..2. .2..2. .0..1
..1..1. .1..1. .2..2. .2..0. .1..2. .1..2. .2..0. .1..2. .1..1. .2..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 15 2016
STATUS
approved