OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 2*a(n-3) + a(n-4).
Empirical g.f.: 2*x*(11 + 7*x + 19*x^2 + 9*x^3) / (1 - x - 2*x^3 - x^4). - Colin Barker, Dec 26 2018
EXAMPLE
Some solutions for n=4:
..1..0..1..0....1..0..1..0....0..1..0..0....0..1..0..1....1..0..1..0
..0..1..0..1....0..1..0..0....1..0..0..0....1..0..1..0....0..1..0..0
..1..0..1..0....1..0..1..0....0..1..0..1....0..1..0..0....1..0..1..0
..0..1..0..0....0..1..0..1....1..0..1..0....1..0..1..0....0..1..0..1
..0..0..1..0....0..0..1..0....0..1..0..0....0..1..0..1....1..0..0..0
..0..1..0..1....0..1..0..1....0..0..1..0....0..0..1..0....0..1..0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jul 04 2015
STATUS
approved