A209000 Number of n-bead necklaces labeled with numbers -1..1 not allowing reversal, with sum zero and first and second differences in -1..1.

1, 1, 1, 1, 1, 2, 3, 5, 7, 10, 13, 20, 29, 51, 85, 155, 265, 471, 803, 1408, 2437, 4309, 7599, 13590, 24231, 43506, 77953, 140219, 252095, 454761, 820873, 1485835, 2691995, 4887096, 8879875, 16158907, 29429535, 53665336

Offset

1,6

Comments

Column 1 of A209007.

Links

Table of n, a(n) for n=1..38.

Example

All solutions for n=11:
.-1...-1...-1...-1...-1....0...-1...-1...-1...-1...-1...-1...-1
.-1...-1...-1...-1...-1....0...-1...-1...-1...-1...-1...-1...-1
.-1....0...-1....0...-1....0....0....0...-1...-1...-1....0....0
.-1....0....0....0....0....0....0....1....0....0...-1....0....0
..0....0....1....0....0....0....0....1....0....0....0....1....0
..0....0....1....1....1....0....0....0....0....0....1....1....0
..1....0....1....1....1....0....1....0....0....1....1....0....0
..1....0....0....0....1....0....1....0....1....1....1....0....1
..1....1....0....0....0....0....0....0....1....1....1....0....1
..1....1....0....0....0....0....0....0....1....0....0....0....0
..0....0....0....0....0....0....0....0....0....0....0....0....0

Crossrefs

Sequence in context: A023192 A064480 A274111 * A115024 A167050 A308388

Adjacent sequences: A208997 A208998 A208999 * A209001 A209002 A209003

Keyword

nonn

Author

R. H. Hardin, Mar 04 2012

Status

approved