OFFSET
1,1
COMMENTS
Column 2 of A267471.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 8*a(n-1) -23*a(n-2) +28*a(n-3) -12*a(n-4).
Conjectures from Colin Barker, Feb 05 2018: (Start)
G.f.: x*(3 - 15*x + 21*x^2 - 7*x^3) / ((1 - x)*(1 - 2*x)^2*(1 - 3*x)).
a(n) = 2^n + 3^(n-1) + 2^(n-2)*(n+1) - 1.
(End)
EXAMPLE
Some solutions for n=7:
..2....1....2....1....2....2....1....1....1....0....1....0....0....1....1....2
..1....0....1....0....1....2....2....0....1....1....2....1....1....2....2....2
..0....2....0....1....0....2....0....1....0....0....2....1....2....2....1....1
..1....2....1....0....1....0....1....2....1....1....1....0....1....2....0....1
..2....2....2....2....1....1....0....2....1....0....0....0....0....1....1....2
..2....0....1....0....0....0....2....1....1....1....0....0....1....2....2....2
..1....2....2....1....0....1....0....1....1....0....1....0....1....0....2....2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 15 2016
STATUS
approved