OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) - a(n-2) + a(n-3) - 2*a(n-4).
Empirical g.f.: x*(4 - 3*x - x^2 - 2*x^3) / ((1 - x)*(1 - 2*x - x^2 - 2*x^3)). - Colin Barker, Sep 27 2018
EXAMPLE
Some solutions for n=4:
..0..1..1....0..0..0....0..0..1....0..0..1....0..1..1....0..0..0....0..0..1
..0..1..1....0..0..0....0..0..1....0..0..1....0..1..1....1..1..0....0..0..1
..0..2..2....0..0..0....0..0..1....0..1..1....0..1..1....1..1..0....2..2..1
..0..2..2....0..0..0....0..1..1....0..1..1....0..0..1....1..1..0....2..2..1
..0..2..2....0..0..0....0..1..1....0..0..0....0..0..1....1..1..0....2..2..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 05 2013
STATUS
approved