OFFSET
1,2
COMMENTS
Column 2 of A216991.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 7*a(n-1) - 9*a(n-2) + a(n-3).
Empirical g.f.: 2*x^2 / (1 - 7*x + 9*x^2 - x^3). - Colin Barker, Jul 23 2018
EXAMPLE
Some solutions for n=3 (movement: 0=n 1=e 2=s 3=w):
..2..2....2..2....1..2....2..3....2..3....1..2....1..2....1..2....2..3....2..3
..1..2....2..3....1..2....1..0....1..0....0..3....0..2....0..3....1..2....2..0
..0..3....1..0....0..3....1..0....0..3....0..0....0..3....1..0....0..3....1..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 21 2012
STATUS
approved