OFFSET
1,2
COMMENTS
Row 2 of A220738.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 2*a(n-1) + 2*a(n-2) - 2*a(n-4) - 2*a(n-5) + a(n-6).
Empirical g.f.: x*(1 - x^2 - x^3 - 2*x^4 + x^5) / ((1 - x)*(1 + x)*(1 - 3*x + x^2)*(1 + x + x^2)). - Colin Barker, Aug 03 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):
.69.47.00...00.69.47...00.67.47...69.49.00...00.00.00
.36.14.00...00.36.14...36.34.00...00.16.14...00.00.00
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 18 2012
STATUS
approved