OFFSET
1,1
COMMENTS
Column 3 of A208408.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 70*a(n-1) - 441*a(n-2) for n>3.
Conjectures from Colin Barker, Jul 02 2018: (Start)
G.f.: x*(5 - 168*x + 147*x^2) / ((1 - 7*x)*(1 - 63*x)).
a(n) = (2/27)*7^(-1+n) * (27+4*9^n) for n>1.
(End)
EXAMPLE
Some solutions for n=4:
..0..0..0....0..0..0....0..0..0....0..0..0....0..1..1....0..0..0....0..0..0
..1..1..0....0..1..0....0..1..1....0..1..0....1..0..2....0..1..0....0..1..1
..0..1..0....1..2..1....1..0..0....0..1..1....3..0..1....2..1..1....2..0..2
..0..1..0....0..1..3....0..1..1....2..0..2....1..1..1....2..1..1....2..1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 26 2012
STATUS
approved