OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-3) - 4*a(n-6) + a(n-9) for n>12.
Empirical g.f.: x*(4682 + 1496*x + 1341*x^2 - 17253*x^3 - 4090*x^4 - 3008*x^5 + 15606*x^6 + 2244*x^7 + 975*x^8 - 3705*x^9 - 344*x^10 - 8*x^11) / ((1 - x)*(1 + x + x^2)*(1 - 3*x^3 + x^6)). - Colin Barker, Dec 03 2018
EXAMPLE
Some solutions for n=4:
..3..1..2..0..1..2..3..1....2..3..0..2..1..3..2..1....0..1..2..0..1..2..0..1
..1..0..2..1..0..2..1..0....0..1..2..0..1..2..0..1....0..0..3..0..0..3..0..0
..0..0..0..0..3..0..0..0....0..0..0..0..0..3..0..0....2..1..3..2..1..3..2..1
..0..1..2..3..1..2..0..1....2..1..0..2..1..3..2..1....0..1..2..0..1..2..0..1
..1..0..2..1..0..2..1..0....0..1..2..0..1..2..0..1....0..0..3..0..0..3..0..0
..0..3..0..0..0..0..0..3....0..0..0..0..0..3..2..0....2..1..3..2..1..3..1..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2014
STATUS
approved