OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = -a(n-1) + 3*a(n-2) + 3*a(n-3) - a(n-4).
Empirical g.f.: x*(1 + 2*x)*(1 + 3*x - x^2) / (1 + x - 3*x^2 - 3*x^3 + x^4). - Colin Barker, Jan 09 2019
EXAMPLE
Some solutions for n=4:
..0..2..2..0....0..2..2..0....1..1..2..2....0..2..2..1....1..1..2..2
..2..2..1..1....2..2..1..1....0..2..2..0....2..2..1..0....0..2..2..0
..0..2..2..0....0..2..2..1....1..1..2..2....0..2..2..1....0..1..2..2
..2..2..1..1....2..2..1..0....0..2..2..0....2..2..1..0....1..2..2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 20 2015
STATUS
approved