login
A208668
Number of 2n-bead necklaces labeled with numbers 1..5 allowing reversal, with neighbors differing by exactly 1.
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
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: A023624 A123194 A372449 * A243860 A322619 A299900
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 29 2012
EXTENSIONS
a(13)-a(30) from Andrew Howroyd, Mar 19 2017
STATUS
approved