OFFSET
1,2
COMMENTS
Column 2 of A221800.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = a(n-1) +6*a(n-2) +a(n-3) -4*a(n-4).
Empirical g.f.: x*(1 + 4*x + x^2 - 4*x^3) / (1 - x - 6*x^2 - x^3 + 4*x^4). - Colin Barker, Aug 11 2018
EXAMPLE
Some solutions for n=3:
..1..0....1..1....2..1....0..2....1..1....0..1....1..1....0..1....1..1....2..1
..2..1....1..1....0..0....1..1....0..1....1..2....1..2....2..2....2..1....1..0
..1..1....1..1....1..2....2..0....1..2....1..1....0..1....1..0....1..0....1..1
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 26 2013
STATUS
approved