OFFSET
1,3
COMMENTS
Row 5 of A220708.
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) - 14*a(n-3) - 11*a(n-4) + 17*a(n-5) + 5*a(n-6) - 6*a(n-7) for n>11.
Empirical g.f.: x*(1 - 2*x - 2*x^2 + 11*x^3 - 8*x^4 - 6*x^5 + 14*x^6 - 18*x^7 - 3*x^8 + 18*x^9 - 8*x^10) / ((1 - x)*(1 + x)*(1 - 3*x - 6*x^2 + 11*x^3 + 5*x^4 - 6*x^5)). - Colin Barker, Aug 02 2018
EXAMPLE
Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10):
.00.00.00...00.00.00...00.67.47...00.67.47...00.00.00...00.00.00...00.00.00
.00.67.47...00.00.00...36.34.00...36.34.00...00.00.00...00.67.47...00.00.00
.36.34.00...00.00.00...00.00.00...00.00.00...00.67.47...36.34.00...00.00.00
.00.00.00...00.67.47...00.00.00...00.67.47...36.34.00...00.67.47...00.00.00
.00.00.00...36.34.00...00.00.00...36.34.00...00.00.00...36.34.00...00.00.00
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 18 2012
STATUS
approved