A209338 Number of n-bead necklaces labeled with numbers -2..2 allowing reversal, with sum zero with no three beads in a row equal.

1, 3, 4, 15, 40, 146, 514, 2032, 8076, 33310, 138966, 589618, 2525494, 10923868, 47599638, 208824200, 921391230, 4086463748, 18206487792

Offset

1,2

Comments

Column 2 of A209344.

Links

Table of n, a(n) for n=1..19.

Example

Some solutions for n=10:
.-2...-2...-2...-2...-2...-2...-2...-2...-2...-2...-2...-2...-2...-2...-2...-2
.-1...-2...-2...-1...-2...-1...-2...-1....0...-1....0...-1...-2...-1....0...-1
.-2....2....0...-1....1...-1....2....0....1...-1....1....0....1...-2....0...-1
.-1...-2....0....1....0....1...-2...-1....0....1....0....2....2....0...-1....1
..0...-1...-1....2...-1....1....1....0....2....2...-2....0....1....2....2....2
..2....0....1....1....2....0....2....2....0....0....1...-1....2....1...-2....2
..1....2....2....0...-1....0....0...-1...-1....0...-2....0...-2....1....0....0
..1...-1...-1....1....0....2...-2....1....1...-2....1....2...-1...-1....0...-1
..0....2....2....0....1...-2....1....2...-2....1....1...-1...-1....0....1...-2
..2....2....1...-1....2....2....2....0....1....2....2....1....2....2....2....2

Crossrefs

Sequence in context: A372342 A332051 A209479 * A127144 A042771 A176755

Adjacent sequences: A209335 A209336 A209337 * A209339 A209340 A209341

Keyword

nonn

Author

R. H. Hardin, Mar 06 2012

Status

approved