OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) - 13*a(n-2) + 12*a(n-3) - 4*a(n-4) for n>5.
Empirical g.f.: x*(2 + 14*x - 54*x^2 + 29*x^3 + 20*x^4) / ((1 - x)^2*(1 - 2*x)^2). - Colin Barker, Sep 19 2018
EXAMPLE
Some solutions for n=3:
..0..0..1....0..1..0....0..0..1....0..1..0....0..1..1....0..1..2....0..1..2
..2..3..2....2..2..3....1..2..3....2..3..2....2..3..2....2..3..0....2..1..3
..1..0..1....3..1..0....3..0..1....0..1..2....1..0..1....1..1..2....3..0..2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 26 2013
STATUS
approved