OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 2*a(n-2) - a(n-4).
Empirical g.f.: x*(9 + x - 3*x^2 - 3*x^3) / (1 - 4*x - 2*x^2 + x^4). - Colin Barker, Oct 03 2018
EXAMPLE
Some solutions for n=6:
..1..1....0..0....2..2....1..1....1..1....1..1....2..2....2..2....1..1....0..0
..0..0....1..1....1..1....1..1....0..0....2..2....0..0....1..1....2..2....0..1
..2..2....2..2....2..2....0..0....0..0....1..1....0..2....1..1....2..0....1..2
..1..0....2..1....2..1....1..1....1..2....0..0....2..0....1..2....0..1....2..1
..0..0....1..2....1..2....2..2....2..0....0..0....0..0....2..2....2..2....1..0
..1..2....2..0....2..1....1..0....0..0....0..1....0..0....0..0....2..0....0..0
..2..2....0..0....1..1....0..0....1..1....2..2....0..0....0..0....0..0....0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 21 2013
STATUS
approved