OFFSET
1,1
COMMENTS
Column 4 of A208314.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 9*a(n-1) - 21*a(n-2) + 21*a(n-3) - 9*a(n-4).
Empirical g.f.: 2*x*(4 - 9*x + 9*x^2 - 3*x^3) / (1 - 9*x + 21*x^2 - 21*x^3 + 9*x^4). - Colin Barker, Jun 30 2018
EXAMPLE
Some solutions for n=4:
..0..1..1..1....0..0..1..0....0..0..0..1....0..1..0..1....0..1..0..1
..1..0..1..0....1..1..0..1....0..1..1..0....0..0..1..0....0..0..1..0
..1..1..0..1....1..0..1..0....1..0..0..1....1..1..0..1....0..1..0..1
..1..0..1..0....1..0..1..1....0..1..1..0....0..1..1..0....1..0..1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 25 2012
STATUS
approved