OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 22*a(n-2) - 36*a(n-4) + 16*a(n-6).
Empirical g.f.: 2*x*(1 + 4*x - 2*x^2) / (1 - 22*x^2 + 36*x^4 - 16*x^6). - Colin Barker, Sep 26 2018
EXAMPLE
Some solutions for n=5:
..0..x..1....0..x..0....0..x..1....0..x..0....0..x..1....0..x..0....0..x..1
..x..2..x....x..1..x....x..2..x....x..1..x....x..2..x....x..1..x....x..2..x
..1..x..2....2..x..0....2..x..0....0..x..2....1..x..2....1..x..1....0..x..0
..x..1..x....x..1..x....x..1..x....x..0..x....x..1..x....x..2..x....x..2..x
..2..x..0....2..x..0....2..x..0....2..x..0....0..x..0....2..x..0....0..x..2
..x..2..x....x..0..x....x..0..x....x..2..x....x..2..x....x..0..x....x..0..x
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 04 2013
STATUS
approved