A208667 Number of 2n-bead necklaces labeled with numbers 1..4 allowing reversal, with neighbors differing by exactly 1.

3, 5, 8, 14, 24, 47, 89, 187, 396, 881, 1990, 4645, 10935, 26211, 63320, 154378, 378444, 933023, 2308957, 5735372, 14286908, 35683815, 89324138, 224057919, 563033979, 1417210457, 3572641304, 9018885122, 22796905056, 57692673963, 146167385345, 370710166435

Offset

1,1

Links

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

Formula

a(n) = (2*A208723(n) + A090991(n))/4. - Andrew Howroyd, Mar 19 2017

Example

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

Crossrefs

Column 4 of A208671.

Sequence in context: A245968 A109022 A023596 * A329823 A329742 A078065

Adjacent sequences: A208664 A208665 A208666 * A208668 A208669 A208670

Keyword

nonn

Author

R. H. Hardin, Feb 29 2012

Extensions

a(25)-a(32) from Andrew Howroyd, Mar 19 2017

Status

approved