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A208725
Number of 2n-bead necklaces labeled with numbers 1..6 not allowing reversal, with neighbors differing by exactly 1.
2
5, 9, 16, 35, 78, 210, 551, 1569, 4475, 13078, 38465, 114584, 343026, 1034471, 3134135, 9540969, 29154478, 89407073, 275016292, 848329872, 2623322133, 8130714643, 25252366057, 78577560856, 244933963301, 764707458720, 2391026407058, 7486342546939
OFFSET
1,1
LINKS
FORMULA
a(n) = (1/n) * Sum_{d | n} totient(n/d) * A198636(d). - Andrew Howroyd, Mar 18 2017
EXAMPLE
All solutions for n=3:
..3....2....1....3....5....2....4....1....2....3....4....4....1....2....1....3
..4....3....2....4....6....3....5....2....3....4....5....5....2....3....2....4
..5....4....3....5....5....2....6....1....4....3....4....4....3....2....1....3
..4....3....4....6....6....3....5....2....5....4....5....5....2....3....2....4
..5....4....3....5....5....2....6....1....4....5....4....6....3....4....3....3
..4....3....2....4....6....3....5....2....3....4....5....5....2....3....2....4
CROSSREFS
Column 6 of A208727.
Sequence in context: A208669 A062777 A215331 * A362108 A272742 A273534
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 01 2012
EXTENSIONS
a(17)-a(28) from Andrew Howroyd, Mar 18 2017
STATUS
approved