OFFSET
1,2
COMMENTS
Column 2 of A220652.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + 8*a(n-3) - 6*a(n-4).
Empirical g.f.: x*(1 + x + 8*x^2 - 6*x^3) / (1 - 3*x - 3*x^2 - 8*x^3 + 6*x^4). - Colin Barker, Aug 02 2018
EXAMPLE
Some solutions for n=3 0=self 1=nw 2=n 3=ne 4=w 6=e 7=sw 8=s 9=se (reciprocal directions total 10):
.68.48...68.48...00.78...69.47...00.00...89.00...00.00...69.47...89.00...00.00
.26.24...29.27...39.27...39.18...00.00...28.17...89.78...38.17...29.17...69.47
.00.00...36.14...36.14...00.12...00.00...23.00...23.12...23.00...36.14...36.14
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
STATUS
approved