OFFSET
1,2
COMMENTS
Column 2 of A221683.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) +2*a(n-2) +a(n-3).
Empirical g.f.: x^2*(2 + x) / (1 - 2*x - 2*x^2 - x^3). - Colin Barker, Oct 19 2017
EXAMPLE
Some solutions for n=6
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..1....1....1....1....1....1....1....0....1....0....1....1....1....0....0....1
..2....1....0....0....1....0....2....2....2....1....2....1....2....2....1....0
..0....1....0....0....1....0....2....2....0....1....0....2....1....2....0....0
..1....0....2....0....2....1....2....0....0....0....0....1....2....1....1....1
..0....1....2....1....2....1....1....0....1....1....0....2....1....0....0....0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 22 2013
STATUS
approved