OFFSET
1,2
COMMENTS
Column 2 of A221308.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) - 3*a(n-2) - 2*a(n-4) + a(n-6).
Empirical g.f.: x^2*(5 - 10*x + 6*x^2 - 4*x^3 + 2*x^4) / ((1 - 3*x + x^3)*(1 - x - x^3)). - Colin Barker, Aug 05 2018
EXAMPLE
All solutions for n=3:
..0..0....0..2....2..2....0..2....0..2....2..0....0..2....2..0....0..0....0..0
..2..0....2..2....0..2....0..2....0..2....2..0....2..0....2..2....2..2....2..2
..2..2....0..0....0..0....2..0....0..2....2..0....2..0....0..0....2..0....0..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 09 2013
STATUS
approved