A208668 Number of 2n-bead necklaces labeled with numbers 1..5 allowing reversal, with neighbors differing by exactly 1.

4, 7, 12, 23, 44, 97, 212, 512, 1260, 3251, 8540, 23035, 62780, 173453, 482692, 1353077, 3811364, 10785235, 30625196, 87239999, 249174236, 713416601, 2046945140, 5884580074, 16946835092, 48883925867, 141217957620, 408519816611, 1183291934300, 3431535849813

Offset

1,1

Links

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

Formula

a(n) = (2*A208724(n) + A090993(n))/4. - Andrew Howroyd, Mar 19 2017

Example

All solutions for n=3:
..3....3....1....1....1....2....2....3....1....2....2....4
..4....4....2....2....2....3....3....4....2....3....3....5
..5....3....1....1....3....2....4....3....3....2....4....4
..4....4....2....2....2....3....5....4....4....3....3....5
..5....5....3....1....3....2....4....3....3....4....4....4
..4....4....2....2....2....3....3....4....2....3....3....5

Crossrefs

Column 5 of A208671.

Sequence in context: A187211 A023624 A123194 * A243860 A322619 A299900

Adjacent sequences: A208665 A208666 A208667 * A208669 A208670 A208671

Keyword

nonn

Author

R. H. Hardin, Feb 29 2012

Extensions

a(13)-a(30) from Andrew Howroyd, Mar 19 2017

Status

approved