OFFSET
1,1
COMMENTS
Column 3 of A220621.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 7*a(n-1) - 4*a(n-2) - 10*a(n-3) + 4*a(n-4).
Empirical g.f.: x*(1 + 2*x)*(3 - 6*x + 2*x^2) / (1 - 7*x + 4*x^2 + 10*x^3 - 4*x^4). - 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):
..0..6..4....0..7..0....0..7..0....0..0..0....6..4..0....0..6..4....0..9..7
..0..6..4....3..6..4....3..7..7....0..9..7....0..7..0....6..4..0....0..3..1
..0..0..0....0..6..4....3..3..0....0..3..1....3..0..0....6..4..0....6..4..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 17 2012
STATUS
approved