OFFSET
1,2
COMMENTS
Column 2 of A221273.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..65
FORMULA
Empirical: a(n) = 6*a(n-1) - 10*a(n-2) + 4*a(n-3) - 2*a(n-5).
Empirical g.f.: 2*x^2*(1 - x)*(3 - 7*x + x^2) / (1 - 6*x + 10*x^2 - 4*x^3 + 2*x^5). - Colin Barker, Mar 14 2018
EXAMPLE
Some solutions for n=4:
..0..2....0..0....0..2....2..0....0..2....2..0....0..0....0..2....2..2....0..0
..2..2....0..2....2..0....2..0....0..2....0..2....2..2....0..2....0..0....2..2
..0..2....2..0....2..0....0..2....0..2....2..0....0..2....0..0....0..0....2..0
..0..0....2..2....2..0....2..0....0..2....0..2....2..0....2..2....2..2....2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 08 2013
STATUS
approved