OFFSET
1,2
COMMENTS
Column 3 of A230652
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*(2*x+1)*(x-1) / ( 1-9*x^2+4*x^4 ). - R. J. Mathar, Oct 27 2013
EXAMPLE
Some solutions for n=5
..0..x..0....0..x..0....1..x..1....0..x..0....2..x..2....0..x..0....2..x..2
..x..2..x....x..2..x....x..1..x....x..2..x....x..0..x....x..2..x....x..0..x
..2..x..0....0..x..0....1..x..1....0..x..2....1..x..1....2..x..2....1..x..2
..x..0..x....x..2..x....x..2..x....x..0..x....x..1..x....x..0..x....x..1..x
..2..x..2....0..x..0....0..x..0....2..x..2....1..x..1....2..x..2....1..x..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 27 2013
STATUS
approved