OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 5*a(n-1) - 7*a(n-2) + 3*a(n-3).
Conjectures from Colin Barker, Nov 02 2018: (Start)
G.f.: x*(3 - 10*x + 6*x^2) / ((1 - x)^2*(1 - 3*x)).
a(n) = (7 + 3^n + 2*n) / 4.
(End)
EXAMPLE
All solutions for n=3:
..0....0....0....0....0....0....0....0....0....0
..1....0....1....0....0....1....1....1....0....0
..2....0....2....1....0....2....2....2....0....1
..3....1....0....2....0....0....3....3....0....2
..0....2....1....3....1....3....1....4....0....0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 05 2014
STATUS
approved