A208722 Number of 2n-bead necklaces labeled with numbers 1..n not allowing reversal, with neighbors differing by exactly 1.

0, 1, 4, 15, 52, 210, 796, 3175, 12468, 49288, 194140, 766110, 3019224, 11905330, 46938192, 185111095, 730148332, 2880799554, 11369141308, 44881708072, 177229210656, 700047776214, 2765947680124, 10931565973950, 43215517211240, 170888480306500

Offset

1,3

Links

Andrew Howroyd, Table of n, a(n) for n = 1..100

Example

All solutions for n=4:
..1....1....3....2....1....2....2....2....2....1....1....1....1....1....1
..2....2....4....3....2....3....3....3....3....2....2....2....2....2....2
..1....3....3....2....3....2....4....4....2....3....1....1....3....3....1
..2....4....4....3....2....3....3....3....3....2....2....2....4....2....2
..3....3....3....2....1....2....4....2....4....3....1....3....3....3....1
..2....4....4....3....2....3....3....3....3....4....2....4....2....2....2
..3....3....3....2....3....4....4....4....4....3....1....3....3....3....3
..2....2....4....3....2....3....3....3....3....2....2....2....2....2....2

Crossrefs

Diagonal of A208727.

Sequence in context: A161125 A027295 A371217 * A057332 A230623 A162978

Adjacent sequences: A208719 A208720 A208721 * A208723 A208724 A208725

Keyword

nonn

Author

R. H. Hardin, Mar 01 2012

Extensions

a(13)-a(26) from Andrew Howroyd, Mar 18 2017

Status

approved