OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) - a(n-2) - 3*a(n-3) - 3*a(n-4) - 6*a(n-5) + 2*a(n-7).
Empirical g.f.: 2*x^2*(1 - x + x^3) / (1 - 6*x + x^2 + 3*x^3 + 3*x^4 + 6*x^5 - 2*x^7). - Colin Barker, Feb 07 2019
EXAMPLE
Some solutions for n=4:
..0..3. .0..3. .0..1. .0..1. .0..3. .0..1. .0..3. .0..1. .0..3. .0..3
..1..2. .1..2. .3..2. .3..2. .1..2. .1..2. .1..0. .3..2. .1..2. .1..0
..1..1. .2..1. .3..0. .2..3. .0..1. .0..3. .2..3. .0..3. .0..3. .2..3
..0..0. .3..0. .2..1. .1..0. .0..0. .3..2. .1..2. .1..2. .2..1. .2..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 12 2016
STATUS
approved