A193646 Number of arrays of -6..6 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero

1, 13, 37, 205, 793, 3673, 15481, 68485, 295453, 1291237, 5605489, 24418801, 106183729, 462160957, 2010578005, 8748949309, 38065839625, 165631750345, 720670846249, 3135725035573, 13643790283981, 59365501769941

Offset

1,2

Comments

Column 6 of A193648

Links

R. H. Hardin, Table of n, a(n) for n = 1..200

Formula

Empirical: a(n) = 2*a(n-1) +10*a(n-2) +a(n-3).

Empirical: G.f.: -x*(1+11*x+x^2) / ( -1+2*x+10*x^2+x^3 ). - R. J. Mathar, Feb 19 2015

Example

Some solutions for n=6
..2...-4...-1...-5....1....5....6....0....1....0....6....0....0...-1....0...-2
.-2....4....1....5...-1...-5...-6....0...-1....3...-6....6....3....1....1....2
.-2...-4...-3....2....0....5....0....0....0...-3....2...-6...-3...-3...-1....2
..2....1....3...-2....0....0...-3....2...-3....3...-2....2...-2....3....3...-2
.-5...-1...-5....1....6....4....3...-2....3....6....0...-2....2....5...-3...-3
..5....0....5...-1...-6...-4....0....0...-3...-6....0....2...-2...-5....3....3

Crossrefs

Sequence in context: A155222 A155283 A155282 * A155236 A155277 A090042

Adjacent sequences: A193643 A193644 A193645 * A193647 A193648 A193649

Keyword

nonn

Author

R. H. Hardin Aug 02 2011

Status

approved