OFFSET
1,2
COMMENTS
Column 5 of A220632.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 9*a(n-2) + 7*a(n-3) + 2*a(n-4) - a(n-5).
Empirical g.f.: x*(1 + 3*x - x^2)*(1 + x + x^2) / ((1 + x)*(1 - 5*x - 4*x^2 - 3*x^3 + x^4)). - Colin Barker, Aug 01 2018
EXAMPLE
Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10):
.00.67.46.46.47...00.67.46.47.00...00.00.00.00.00...00.00.67.46.47
.36.47.00.36.47...36.46.34.67.47...00.67.46.47.00...00.37.67.34.00
.36.46.46.34.00...00.00.36.34.00...36.46.34.00.00...36.34.00.00.00
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
STATUS
approved