OFFSET
1,2
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) - 4*a(n-2) for n>3.
Conjectures from Colin Barker, Sep 19 2018: (Start)
G.f.: x*(1 + 2*x + 6*x^2) / (1 - 2*x)^2.
a(n) = 2^(n-2) * (7*n-8) for n>1. (End)
Conjectured e.g.f.: 2 + (3*x + exp(2*x)*(7*x - 4))/2. - Stefano Spezia, Oct 21 2022
EXAMPLE
Some solutions for n=3:
..0..1....0..1....0..0....0..1....0..1....0..1....0..1....0..1....0..1....0..1
..2..2....2..0....1..2....2..2....2..1....2..2....2..2....2..3....2..1....2..2
..0..3....1..3....3..0....0..1....3..0....3..1....3..0....2..0....0..3....1..3
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 26 2013
STATUS
approved