OFFSET
1,2
COMMENTS
Column 2 of A217028.
It seems that all terms are squares. - Colin Barker, Mar 09 2018
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 9*a(n-1) -3*a(n-2) -25*a(n-3) +9*a(n-4) +3*a(n-5) -a(n-6).
Empirical g.f.: x*(1 + 7*x - 20*x^2 + 8*x^3 + 2*x^4 - x^5) / ((1 - 9*x + 6*x^2 - x^3)*(1 - 3*x^2 - x^3)). - Colin Barker, Mar 09 2018
EXAMPLE
Some solutions for n=3 (movement: 0=n 1=e 2=s 3=w):
..2..3....1..2....2..2....2..3....1..3....2..3....2..2....1..2....1..3....2..2
..1..2....0..0....0..2....0..2....0..0....0..0....0..3....0..3....1..3....2..2
..1..3....1..3....1..3....1..3....0..0....0..0....1..3....1..0....0..3....0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 24 2012
STATUS
approved