OFFSET
1,2
COMMENTS
Column 3 of A220688.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) + 12*a(n-2) + 19*a(n-3) + 16*a(n-4) + 2*a(n-5) for n>6.
Empirical g.f.: x*(1 + 6*x + 10*x^2 + 18*x^3 + 9*x^4 + x^5) / ((1 + x)*(1 - 7*x - 5*x^2 - 14*x^3 - 2*x^4)). - Colin Barker, Aug 02 2018
EXAMPLE
Some solutions for n=3 0=self 2=n 3=ne 4=w 6=e 7=sw 8=s (reciprocal directions total 10):
.68.46.47...68.47.00...00.67.48...00.00.00...68.47.00...00.67.48...00.78.00
.28.36.48...23.67.47...36.47.27...68.46.47...23.67.48...38.68.24...38.26.48
.26.46.24...36.34.00...36.34.00...26.34.00...36.46.24...26.24.00...26.46.24
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
STATUS
approved