OFFSET
1,1
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) - 9*a(n-3).
Empirical g.f.: 4*x*(1 - 2*x - 2*x^2) / ((1 - 3*x)*(1 - 3*x - 3*x^2)). - Colin Barker, Jan 28 2019
EXAMPLE
Some solutions for n=8:
..1. .3. .2. .3. .3. .1. .2. .0. .2. .0. .3. .3. .3. .2. .3. .1
..0. .0. .1. .1. .2. .3. .0. .2. .3. .3. .3. .3. .0. .1. .0. .0
..1. .0. .3. .1. .3. .0. .3. .2. .0. .2. .0. .1. .1. .2. .1. .0
..2. .3. .3. .1. .3. .2. .1. .2. .2. .2. .1. .0. .0. .0. .0. .1
..3. .3. .3. .1. .1. .1. .2. .2. .0. .1. .1. .1. .3. .0. .1. .0
..1. .1. .1. .1. .1. .1. .3. .3. .2. .0. .0. .2. .0. .1. .1. .0
..3. .0. .0. .1. .3. .1. .0. .0. .2. .0. .3. .0. .0. .2. .1. .0
..0. .1. .2. .2. .2. .0. .3. .3. .3. .3. .2. .1. .0. .2. .2. .1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 04 2016
STATUS
approved