OFFSET
1,2
COMMENTS
Row 2 of A220725.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 3*a(n-1) + a(n-2) - 2*a(n-4).
Empirical g.f.: x*(1 - x - 2*x^3) / (1 - 3*x - x^2 + 2*x^4). - Colin Barker, Aug 02 2018
EXAMPLE
All solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10):
.00.00.00...00.67.47...69.49.00...00.69.47...69.47.00...69.46.47...00.79.00
.00.00.00...36.34.00...00.16.14...00.36.14...36.14.00...00.13.00...36.46.14
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 18 2012
STATUS
approved