OFFSET
1,1
COMMENTS
Column 3 of A208069.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4) for n>5.
Conjectures from Colin Barker, Jun 27 2018: (Start)
G.f.: 6*x*(1 + 4*x + 2*x^3 - x^4) / ((1 - x)^3*(1 + x)).
a(n) = 9*n^2 for n>1 and even.
a(n) = 9*n^2-9 for n>1 and odd.
(End)
EXAMPLE
Some solutions for n=4:
..0..0..1....1..1..0....1..1..0....0..1..1....1..1..0....0..0..1....0..0..1
..0..1..1....1..0..1....1..1..0....1..1..0....0..0..1....0..1..1....0..0..1
..0..0..1....1..0..0....1..0..0....0..1..1....1..1..0....0..0..1....0..0..1
..0..0..1....0..0..1....1..1..0....1..0..0....0..0..1....0..1..0....0..0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 23 2012
STATUS
approved