OFFSET
1,1
COMMENTS
Column 1 of A230708.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 3*a(n-2) - 6*a(n-3) + a(n-5).
Empirical g.f.: 2*x*(1 + x) / ((1 - x)*(1 - 2*x - 5*x^2 + x^3 + x^4)). - Colin Barker, Mar 17 2018
EXAMPLE
Some solutions for n=2:
..0..x..0..x....0..x..1..x....0..x..0..x....0..x..0..x....0..x..2..x
..x..1..x..1....x..1..x..2....x..1..x..2....x..1..x..2....x..1..x..0
..0..x..2..x....2..x..0..x....2..x..0..x....2..x..1..x....0..x..1..x
..x..2..x..0....x..0..x..2....x..0..x..2....x..0..x..0....x..2..x..0
..1..x..1..x....2..x..1..x....2..x..1..x....2..x..2..x....1..x..2..x
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 28 2013
STATUS
approved