OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) - 3*a(n-2) - 2*a(n-3).
Conjectures from Colin Barker, Jan 27 2019: (Start)
G.f.: 3*x*(1 - x) / ((1 - 2*x)*(1 - 2*x - x^2)).
a(n) = 3*(-2^(1+n) + (1-sqrt(2))^(1+n) + (1+sqrt(2))^(1+n)) / 2.
(End)
EXAMPLE
Some solutions for n=9:
..0. .2. .0. .2. .1. .0. .0. .2. .0. .1. .1. .1. .1. .0. .2. .2
..2. .0. .0. .0. .0. .0. .2. .2. .0. .2. .0. .0. .2. .1. .1. .1
..1. .2. .2. .1. .0. .0. .1. .1. .1. .0. .1. .2. .0. .0. .2. .0
..1. .2. .0. .2. .2. .1. .0. .2. .0. .2. .0. .0. .1. .1. .0. .0
..1. .2. .2. .0. .1. .2. .1. .2. .0. .1. .1. .0. .1. .0. .1. .0
..2. .0. .0. .1. .2. .1. .1. .0. .0. .1. .0. .0. .2. .2. .1. .0
..0. .1. .2. .0. .1. .0. .2. .1. .0. .2. .1. .0. .0. .1. .2. .1
..1. .2. .1. .2. .2. .1. .1. .2. .0. .0. .1. .0. .1. .0. .1. .0
..1. .1. .2. .1. .0. .2. .2. .1. .0. .1. .1. .2. .0. .2. .0. .2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 03 2016
STATUS
approved