A208771 Number of n-bead necklaces labeled with numbers 1..n not allowing reversal, with no adjacent beads differing by more than 1.

1, 3, 7, 18, 41, 117, 299, 861, 2413, 6955, 19943, 57974, 168013, 489789, 1428611, 4177232, 12226997, 35847123, 105200351, 309086838, 908931221, 2675276801, 7880255915, 23228969891, 68518137777, 202231890207, 597228362551, 1764663912122

Offset

1,2

Links

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

Example

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

Crossrefs

Diagonal of A208777.

Sequence in context: A131630 A305652 A356938 * A036884 A102291 A034691

Adjacent sequences: A208768 A208769 A208770 * A208772 A208773 A208774

Keyword

nonn

Author

R. H. Hardin, Mar 01 2012

Extensions

a(19)-a(28) from Andrew Howroyd, Mar 18 2017

Status

approved