OFFSET
1,1
COMMENTS
Column 5 of A220562.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 21*a(n-1) - 62*a(n-2) + 47*a(n-3) - 5*a(n-4) for n>5.
Empirical g.f.: x*(8 - 19*x - 29*x^2 + 144*x^3 - 23*x^4) / ((1 - x)*(1 - 20*x + 42*x^2 - 5*x^3)). - 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..0..6..4....0..0..0..6..4....0..0..0..6..4....0..0..6..4..0
..6..4..0..6..4....0..6..4..0..0....0..6..4..7..0....0..7..7..7..0
..0..6..4..0..0....0..6..4..0..0....0..0..3..0..0....3..3..3..0..0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 16 2012
STATUS
approved