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) + 6*a(n-3) - 8*a(n-4).
Empirical g.f.: x*(1 + 2*x)*(2 + x - 4*x^2) / (1 - 3*x + x^2 - 6*x^3 + 8*x^4). - Colin Barker, Feb 22 2019
EXAMPLE
Some solutions for n=7:
..0..1. .0..0. .1..0. .0..0. .1..0. .0..0. .0..0. .1..0. .0..1. .0..1
..0..1. .0..0. .0..1. .0..0. .0..1. .0..1. .1..1. .1..0. .0..1. .0..1
..1..0. .1..0. .0..1. .0..1. .0..0. .1..1. .0..1. .0..0. .0..1. .0..0
..1..0. .1..0. .0..0. .1..0. .1..0. .0..0. .0..0. .1..0. .0..0. .1..1
..0..1. .1..0. .1..0. .0..0. .1..0. .1..0. .1..0. .1..1. .1..0. .0..0
..1..0. .0..1. .1..0. .1..1. .0..1. .1..1. .1..0. .0..0. .0..1. .1..1
..0..1. .0..0. .0..0. .1..0. .1..0. .0..0. .0..1. .1..1. .0..0. .1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 29 2017
STATUS
approved