A209337 Number of n-bead necklaces labeled with numbers -1..1 allowing reversal, with sum zero with no three beads in a row equal.

1, 2, 1, 4, 5, 14, 21, 51, 102, 249, 555, 1358, 3201, 7890, 19232, 47869, 118955, 298875, 752039, 1904621, 4835666, 12330144, 31521037, 80836979, 207803455, 535535393, 1383064966, 3579351724, 9280561947

Offset

1,2

Comments

Column 1 of A209344.

Links

Table of n, a(n) for n=1..29.

Example

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

Crossrefs

Sequence in context: A350087 A091232 A336398 * A243004 A375156 A137424

Adjacent sequences: A209334 A209335 A209336 * A209338 A209339 A209340

Keyword

nonn

Author

R. H. Hardin, Mar 06 2012

Status

approved