OFFSET
1,2
COMMENTS
Row 2 of A221275.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..94
FORMULA
Empirical: a(n) = 4*a(n-1) - 12*a(n-3) + 9*a(n-4).
Empirical g.f.: x^2*(2 - 3*x)^2 / ((1 - x)*(1 - 3*x)*(1 - 3*x^2)). - Colin Barker, Aug 04 2018
EXAMPLE
Some solutions for n=4:
..0..0..0..2....0..2..2..0....2..2..2..0....2..0..0..0....0..2..2..0
..2..2..2..0....2..0..0..2....0..0..0..2....0..2..2..2....0..2..2..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 09 2013
STATUS
approved