OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 8*a(n-1) - 21*a(n-2) + 22*a(n-3) - 8*a(n-4).
Conjectures from Colin Barker, Nov 02 2018: (Start)
G.f.: x*(3 - 19*x + 33*x^2 - 16*x^3) / ((1 - x)^2*(1 - 2*x)*(1 - 4*x)).
a(n) = (26 + 9*2^n + 4^n + 6*n) / 18.
(End)
EXAMPLE
All solutions for n=3:
..0....0....0....0....0....0....0....0....0....0
..1....0....0....0....1....1....1....1....0....0
..2....1....0....1....2....2....2....2....0....0
..0....2....1....2....3....3....3....0....0....0
..1....0....2....3....1....0....4....3....1....0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 05 2014
STATUS
approved