OFFSET
1,2
COMMENTS
Row 3 of A220562.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 4*a(n-1) + 15*a(n-2) - 5*a(n-3) - 19*a(n-4) + 9*a(n-5) + 2*a(n-6) - a(n-7).
Empirical g.f.: x*(1 - x)*(1 + 10*x + 7*x^2 - 9*x^3 - x^4 + x^5) / ((1 + x - x^2)*(1 - 5*x - 9*x^2 + 9*x^3 + x^4 - x^5)). - 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):
..0..6..4....6..4..0....0..7..0....0..7..7....0..6..4....6..4..7....0..0..0
..6..4..0....0..7..0....3..0..0....3..3..7....0..0..0....0..3..7....6..4..0
..0..6..4....3..0..0....6..4..0....0..3..0....0..0..0....0..3..0....0..6..4
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 16 2012
STATUS
approved