OFFSET
1,2
COMMENTS
Column 5 of A220614.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 6*a(n-2) - 11*a(n-3) - 5*a(n-4) + 6*a(n-5).
Empirical g.f.: x*(1 + 5*x - 9*x^2 - 5*x^3 + 6*x^4) / (1 - 3*x - 6*x^2 + 11*x^3 + 5*x^4 - 6*x^5). - Colin Barker, Aug 01 2018
EXAMPLE
Some solutions for n=3 0=self 2=n 4=w 6=e 8=s (reciprocal directions total 10):
.00.00.00.00.00...00.00.68.48.00...68.48.00.00.00...00.00.00.00.00
.68.48.00.68.48...68.48.26.24.00...26.24.68.48.00...00.00.00.68.48
.26.24.00.26.24...26.24.00.00.00...00.00.26.24.00...00.00.00.26.24
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
STATUS
approved