OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 8*a(n-1) - 20*a(n-2) + 12*a(n-3) + 12*a(n-4) - 8*a(n-5) - 3*a(n-6).
Empirical g.f.: x*(1 - 6*x + 9*x^2 + 2*x^3 - 4*x^4 - x^5) / ((1 - x)*(1 - 3*x)*(1 - x - x^2)*(1 - 3*x - x^2)). - Colin Barker, Jan 13 2019
EXAMPLE
Some solutions for n=8:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....1....1....1....0....1....1....1....1....0....1....1....1....1....0....1
..0....2....1....2....0....0....1....2....0....1....0....2....0....2....0....0
..1....2....0....2....0....1....1....1....2....2....2....0....2....1....1....1
..2....3....2....1....0....2....0....2....3....0....1....0....0....3....0....1
..0....0....3....0....0....1....1....3....3....2....3....2....3....0....2....1
..3....2....0....3....0....0....2....3....3....0....1....0....2....2....1....2
..0....2....3....2....1....3....3....2....1....1....0....2....2....0....0....1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 04 2016
STATUS
approved