OFFSET
1,1
COMMENTS
Column 4 of A220562.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 11*a(n-1) - 17*a(n-2) + 7*a(n-3) - a(n-4).
Empirical g.f.: x*(5 - 8*x - 2*x^2) / (1 - 11*x + 17*x^2 - 7*x^3 + x^4). - Colin Barker, Jul 31 2018
EXAMPLE
Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10):
..0..0..6..4....6..4..0..0....0..7..0..0....0..0..6..4....0..7..7..7
..6..4..6..4....0..6..4..0....3..0..6..4....0..0..0..0....3..3..3..7
..0..6..4..0....0..0..0..0....6..4..6..4....6..4..0..0....6..4..3..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 16 2012
STATUS
approved