OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + a(n-3) - 3*a(n-4).
Empirical g.f.: x*(3 - 2*x - 2*x^2 - 3*x^3) / ((1 - x)*(1 - 3*x)*(1 + x + x^2)). - Colin Barker, Jan 01 2019
EXAMPLE
Some solutions for n=4:
..0..0..0....2..2..2....2..2..2....1..1..1....0..0..0....1..1..1....1..1..1
..1..1..1....0..0..0....2..2..2....2..2..2....2..2..2....2..2..2....1..1..1
..0..0..0....2..2..2....1..1..1....2..2..2....0..0..0....2..2..2....1..1..1
..2..2..2....0..0..0....1..1..1....1..1..1....0..0..0....2..2..2....2..2..2
..1..1..1....2..2..2....1..1..1....0..0..0....2..2..2....1..1..1....2..2..2
..2..2..2....0..0..0....2..2..2....0..0..0....1..1..1....1..1..1....2..2..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 15 2015
STATUS
approved