OFFSET
1,2
COMMENTS
Row 3 of A220621.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 6*a(n-1) + 22*a(n-2) - 32*a(n-3) - 12*a(n-4) + 8*a(n-5) - 3*a(n-6).
Empirical g.f.: x*(1 + 16*x - 29*x^2 - 13*x^3 + 8*x^4 - 3*x^5) / (1 - 6*x - 22*x^2 + 32*x^3 + 12*x^4 - 8*x^5 + 3*x^6). - Colin Barker, Aug 01 2018
EXAMPLE
Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10):
..6..4..0....0..6..4....0..7..0....0..0..0....6..4..0....0..7..0....0..7..0
..0..0..0....0..6..4....3..6..4....0..0..0....9..9..0....3..6..4....3..0..7
..0..0..0....6..4..0....0..6..4....0..6..4....0..1..1....0..0..0....0..3..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
STATUS
approved