OFFSET
1,1
COMMENTS
Column 3 of A230989.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + 3*a(n-2) - 3*a(n-3) - 6*a(n-4) + 2*a(n-5) + 4*a(n-6) - a(n-7) - a(n-8).
Empirical g.f.: x*(2 - 3*x^2 - 4*x^3 + 2*x^4 + 2*x^5 - x^6) / (1 - 2*x - 3*x^2 + 3*x^3 + 6*x^4 - 2*x^5 - 4*x^6 + x^7 + x^8). - Colin Barker, Mar 18 2018
EXAMPLE
Some solutions for n=6:
..0..x..0..x....0..x..1..x....0..x..0..x....0..x..1..x....0..x..0..x
..x..1..x..1....x..1..x..0....x..1..x..0....x..1..x..0....x..1..x..1
..1..x..0..x....0..x..1..x....1..x..1..x....1..x..0..x....0..x..0..x
..x..0..x..0....x..1..x..0....x..0..x..0....x..0..x..1....x..1..x..1
..1..x..1..x....0..x..0..x....1..x..1..x....1..x..0..x....1..x..0..x
..x..0..x..1....x..0..x..1....x..0..x..0....x..1..x..1....x..0..x..1
..1..x..0..x....1..x..1..x....1..x..1..x....0..x..0..x....1..x..1..x
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 02 2013
STATUS
approved