A209067 Number of n-bead necklaces labeled with numbers -2..2 not allowing reversal, with sum zero and avoiding the pattern z z+1 z+2.

1, 3, 6, 22, 70, 265, 1007, 4055, 16593, 69429, 294509, 1265692, 5494398, 24065829, 106207739, 471840078, 2108406146, 9470071142, 42731427358, 193612759011, 880517540867

Offset

1,2

Comments

Column 2 of A209073.

Links

Table of n, a(n) for n=1..21.

Example

Some solutions for n=6:
.-2...-2...-2...-2...-2...-2...-1...-2...-2...-2...-2...-2...-2...-2...-2...-1
..1...-1....2....1...-1....1...-1...-1....2....0....1....1....0...-2...-1...-1
..2....1....0....0...-1....0....1...-2...-1...-1....1...-1....0...-2....2....0
..0....1...-1....1....2....2...-1....1....2....1....0....1....1....2...-1....0
..0...-1....2...-2....1....0....0....2....0....0...-2....1....1....2....0....0
.-1....2...-1....2....1...-1....2....2...-1....2....2....0....0....2....2....2

Crossrefs

Sequence in context: A380061 A049415 A208939 * A220166 A220167 A378731

Adjacent sequences: A209064 A209065 A209066 * A209068 A209069 A209070

Keyword

nonn

Author

R. H. Hardin, Mar 04 2012

Status

approved