OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + 2*a(n-2) - a(n-3) + 2*a(n-4) - 3*a(n-5) - a(n-6) for n>12.
Empirical g.f.: x*(1 + 2*x + x^2 - 2*x^3 - 4*x^4 - 6*x^5 - 3*x^6 + 4*x^7 - 5*x^8 + 2*x^9 - x^10 + x^11) / ((1 - x)*(1 + x^2)*(1 - x - 4*x^2 - x^3)). - Colin Barker, Jan 09 2019
EXAMPLE
Some solutions for n=4:
..0..1..2..2..1....0..1..2..2..0....1..1..2..2..1....1..1..2..2..2
..1..2..2..1..0....1..2..2..1..1....0..2..2..1..0....0..2..0..2..2
..0..1..2..2..1....0..1..2..2..0....1..1..2..2..1....2..2..0..2..0
..1..2..2..1..0....1..2..2..1..1....0..2..2..1..0....2..2..2..1..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 20 2015
STATUS
approved