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>15.
Empirical g.f.: x*(904 + 764*x + 984*x^2 - 2519*x^3 - 1389*x^4 - 1580*x^5 + 1997*x^6 + 610*x^7 + 504*x^8 - 456*x^9 - 73*x^10 - 4*x^11 - 4*x^12 - 4*x^13 - x^14) / ((1 - x)*(1 + x + x^2)*(1 - 3*x^3 + x^6)). - Colin Barker, Dec 03 2018
EXAMPLE
Some solutions for n=4:
..2..1..0..2..1..3....0..0..0..0..0..3....2..0..1..2..0..1....0..3..0..0..3..0
..0..0..0..0..3..0....1..2..0..1..2..0....2..1..3..2..1..0....3..1..2..3..1..2
..2..0..1..2..0..1....0..2..1..3..2..1....0..3..0..0..0..0....1..0..2..1..0..2
..2..1..3..2..1..0....0..0..3..0..0..0....2..0..1..2..0..1....0..3..0..0..3..0
..0..3..0..0..0..0....1..2..0..1..2..3....2..1..0..2..1..3....3..1..2..3..1..2
..2..0..1..2..0..1....3..2..1..0..2..1....0..0..0..0..3..0....1..0..2..1..0..2
..2..1..0..2..1..3....0..0..0..3..0..0....2..0..1..2..0..1....0..3..0..0..3..0
..0..0..0..0..3..0....1..2..3..1..2..0....2..1..3..2..1..0....3..1..2..3..1..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2014
STATUS
approved