OFFSET
1,2
COMMENTS
Column 3 of A230661
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 9*a(n-2) -4*a(n-4).
Empirical: G.f. -3*x^2*(-1-5*x+2*x^2) / ( 1-9*x^2+4*x^4 ). - R. J. Mathar, Oct 27 2013
EXAMPLE
Some solutions for n=5
..x..0..x....x..2..x....x..1..x....x..0..x....x..2..x....x..2..x....x..2..x
..1..x..2....0..x..0....0..x..1....2..x..0....0..x..0....2..x..0....0..x..0
..x..1..x....x..0..x....x..2..x....x..2..x....x..2..x....x..0..x....x..1..x
..2..x..2....2..x..0....1..x..0....0..x..2....0..x..0....0..x..0....0..x..1
..x..0..x....x..2..x....x..1..x....x..0..x....x..2..x....x..2..x....x..2..x
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 27 2013
STATUS
approved