OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) - 4*a(n-2) + 2*a(n-3) - a(n-4).
Empirical g.f.: x*(13 - 17*x + 8*x^2 - 5*x^3) / ((1 - x)*(1 - 3*x + x^2 - x^3)). - Colin Barker, Nov 02 2018
EXAMPLE
Some solutions for n=3:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....0....1....0....1....1....1....0....1....1....1....0....0....0....0
..0....1....1....0....1....2....0....1....0....0....0....2....1....1....1....1
..1....2....1....2....0....0....2....1....1....2....2....2....2....2....0....2
..0....2....2....0....1....2....1....1....2....1....1....2....1....0....2....1
..1....2....2....0....0....0....0....2....0....1....2....0....0....0....2....1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 04 2014
STATUS
approved