OFFSET
1,1
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..60
FORMULA
Empirical: a(n) = a(n-1) + 6*a(n-2) - 6*a(n-3) - 10*a(n-4) + 10*a(n-5) + 4*a(n-6) - 4*a(n-7).
Empirical g.f.: 2*x*(18 + 7*x - 97*x^2 - 21*x^3 + 149*x^4 + 10*x^5 - 58*x^6) / ((1 - x)*(1 - 2*x^2)*(1 - 4*x^2 + 2*x^4)). - Colin Barker, Jul 19 2018
EXAMPLE
Some solutions for n=5:
.-2....0....3....2....0...-3...-1....0....2....1...-2...-2...-2....0...-2...-3
.-1...-3....2...-1...-1...-1...-2...-3....3....0...-1...-1...-3....3...-1...-2
..0....0....1....2...-2...-3...-1....0....2...-1....0....0...-2....0...-2...-3
..1....3....0...-1...-3...-1...-2....3....1....0...-1....1...-1....3...-1...-2
..0....0....1....2...-2...-3...-1....0....2....1....0....2...-2....0....0...-1
..1...-3....0...-1...-1...-1....0....3....3....2....1....1...-3....3...-1...-2
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Apr 20 2012
STATUS
approved