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

Author

R. H. Hardin, Mar 01 2012

Keywords

• nonn

Examples

			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
		

Links

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

Crossrefs

Diagonal of A208727.

Extensions

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