OFFSET
1,2
COMMENTS
Column 2 of A220718.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + 8*a(n-2) + 3*a(n-3) - 2*a(n-4) - 3*a(n-5) + a(n-6).
Empirical g.f.: x*(1 + 6*x + 2*x^2 - x^3 - 3*x^4 + x^5) / (1 - 2*x - 8*x^2 - 3*x^3 + 2*x^4 + 3*x^5 - x^6). - 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):
.69.47...68.47...89.00...00.00...00.00...00.00...00.78...69.48...00.00...89.78
.36.14...23.00...29.17...69.47...68.48...00.78...39.27...00.12...68.47...23.12
.00.00...00.00...36.14...36.14...26.24...36.24...36.14...00.00...23.00...00.00
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 18 2012
STATUS
approved