OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) + 2*a(n-3) - 2*a(n-4).
Empirical g.f.: 4*x*(4 + x + x^2 - 7*x^3) / ((1 - x)*(1 - 2*x^3)). - Colin Barker, Nov 08 2018
EXAMPLE
Some solutions for n=6:
..1....1....1....2....2....0....1....1....2....3....2....1....1....0....0....3
..0....3....2....1....0....1....0....3....0....2....0....3....1....1....0....1
..2....2....3....3....1....2....2....2....1....1....1....2....1....2....0....2
..1....1....1....2....2....3....1....1....2....3....2....1....1....0....0....0
..0....0....2....1....0....1....3....0....0....2....3....3....1....1....0....1
..2....2....3....0....1....2....2....2....1....1....1....2....1....2....0....2
..1....1....1....2....2....3....1....1....2....0....2....1....1....3....0....3
..0....0....2....1....3....1....3....3....0....2....3....0....1....1....0....1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 06 2014
STATUS
approved