OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 4*a(n-3).
Empirical g.f.: 2*x*(1 + 2*x^2) / ((1 - 2*x)*(1 + x + 2*x^2)). - Colin Barker, Jan 09 2019
EXAMPLE
Some solutions for n=4:
..1..1..0....0..1..0....1..1..0....1..1..0....0..1..1....0..2..2....0..1..0
..0..2..2....1..2..2....0..1..0....0..2..2....0..2..2....2..2..1....1..2..2
..2..2..1....2..2..0....1..2..2....2..2..0....2..2..1....0..1..0....2..2..0
..0..1..0....1..1..0....2..2..0....1..1..0....0..1..0....0..1..1....0..1..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 20 2015
STATUS
approved