OFFSET
1,2
COMMENTS
Column 2 of A220595.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + 7*a(n-2) + 2*a(n-3) - 2*a(n-4).
Empirical g.f.: x*(1 + x)*(1 + 4*x - 2*x^2) / (1 - 3*x - 7*x^2 - 2*x^3 + 2*x^4). - Colin Barker, Aug 01 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...00.00...00.00...00.00...69.47...68.48...89.00...69.48...00.00...68.48
.39.17...69.48...00.78...68.48...39.18...29.27...29.17...00.12...69.47...28.28
.36.14...00.12...36.24...26.24...00.12...36.14...36.14...00.00...36.14...26.24
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 16 2012
STATUS
approved