OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + a(n-3).
Empirical g.f.: 4*x*(15 + 3*x + 7*x^2) / (1 - 2*x - x^3). - Colin Barker, Nov 06 2018
EXAMPLE
Some solutions for n=6:
..2....3....2....1....0....2....1....0....0....2....1....3....2....0....2....1
..0....3....2....1....2....2....3....0....2....0....1....3....3....0....2....3
..0....2....2....0....0....2....1....0....2....2....1....3....2....0....3....1
..2....2....2....1....0....2....1....0....2....2....0....3....3....1....3....3
..0....2....3....1....0....2....1....0....2....2....0....1....2....1....2....3
..0....2....3....0....0....2....1....0....3....0....0....1....2....1....3....3
..0....2....3....0....0....3....1....2....3....0....1....1....2....3....3....3
..0....0....3....1....0....2....3....0....3....0....0....3....2....1....2....1
..1....0....2....0....0....3....1....2....2....0....1....1....0....3....2....3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Aug 27 2014
STATUS
approved