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A208667
Number of 2n-bead necklaces labeled with numbers 1..4 allowing reversal, with neighbors differing by exactly 1.
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
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 29 2012
EXTENSIONS
a(25)-a(32) from Andrew Howroyd, Mar 19 2017
STATUS
approved