OFFSET
1,2
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) - 4*a(n-4).
Empirical g.f.: x*(1 + x)^2*(1 - 2*x) / ((1 - x)*(1 - x - 4*x^2 - 4*x^3)). - Colin Barker, Sep 28 2018
EXAMPLE
Some solutions for n=4:
..0..0....0..0....0..0....0..0....0..0....0..0....0..0....0..0....0..0....0..0
..0..0....0..0....0..1....0..1....0..1....0..0....0..0....0..0....0..0....0..0
..0..1....1..1....1..1....1..1....1..1....0..0....1..1....1..1....0..0....0..0
..1..1....1..1....0..0....2..2....1..1....0..1....1..2....1..0....1..1....0..0
..1..1....1..1....0..0....2..2....1..1....1..1....2..2....0..0....1..1....0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 07 2013
STATUS
approved