OFFSET
1,1
COMMENTS
Column 2 of A218663.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + 3*a(n-3).
Empirical g.f.: 3*x*(1 + x)^2 / (1 - 3*x - 3*x^2 - 3*x^3). - Colin Barker, Mar 10 2018
EXAMPLE
Some solutions for n=3:
..1..1....1..1....1..0....0..0....1..1....0..1....0..1....0..0....1..1....0..0
..1..1....1..0....1..1....0..1....0..1....0..0....1..0....1..0....0..1....0..1
..1..1....0..1....1..1....0..0....0..1....1..0....0..1....1..1....0..0....0..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 04 2012
STATUS
approved