OFFSET
1,2
COMMENTS
Column 2 of A240642.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) + 10*a(n-2) - 6*a(n-3) - 9*a(n-4) for n>6.
Empirical g.f.: x*(1 - x - 13*x^2 - 13*x^3 + 2*x^4 + 3*x^5) / ((1 - x)*(1 + x)*(1 - 6*x - 9*x^2)). - Colin Barker, Mar 19 2018
EXAMPLE
Some solutions for n=4:
..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1
..1..0....1..2....2..0....1..0....2..3....1..0....2..0....2..0....2..3....1..2
..2..1....3..1....0..2....2..1....0..2....2..2....3..2....0..2....0..1....2..1
..3..0....2..3....3..1....0..2....3..0....2..2....0..1....1..0....1..3....0..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Apr 09 2014
STATUS
approved