OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 5*a(n-1) - 5*a(n-2) - 8*a(n-3) + 12*a(n-4).
Empirical g.f.: x*(3 - 6*x - 6*x^2 + 11*x^3) / ((1 - 2*x)^2*(1 - x - 3*x^2)). - Colin Barker, Jan 24 2019
EXAMPLE
Some solutions for n=7:
..2. .2. .2. .2. .2. .0. .1. .0. .2. .2. .2. .1. .0. .1. .2. .2
..1. .1. .1. .1. .0. .2. .2. .2. .0. .0. .1. .2. .2. .2. .0. .1
..2. .1. .0. .2. .2. .1. .1. .2. .0. .1. .0. .2. .1. .1. .1. .0
..0. .2. .2. .1. .1. .0. .1. .1. .2. .1. .1. .0. .0. .0. .0. .1
..1. .1. .0. .0. .0. .2. .2. .0. .0. .0. .0. .1. .2. .1. .1. .2
..1. .0. .1. .2. .2. .0. .0. .2. .1. .1. .0. .2. .1. .0. .0. .1
..2. .1. .0. .0. .1. .0. .1. .0. .2. .2. .2. .0. .1. .2. .1. .0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 01 2016
STATUS
approved