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A208545 Number of 7-bead necklaces of n colors allowing reversal, with no adjacent beads having the same color 1
0, 0, 9, 156, 1170, 5580, 19995, 58824, 149796, 341640, 714285, 1391940, 2559414, 4482036, 7529535, 12204240, 19173960, 29309904, 43730001, 63847980, 91428570, 128649180, 178168419, 243201816, 327605100, 435965400, 573700725, 747168084 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Row 7 of A208544

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = (1/14)*n^7 - (1/2)*n^6 + (3/2)*n^5 - (5/2)*n^4 + (5/2)*n^3 - (3/2)*n^2 + (3/7)*n

EXAMPLE

All solutions for n=3

..1....1....1....1....1....1....1....1....1

..2....2....2....2....2....2....2....2....2

..3....3....1....1....3....1....3....1....3

..1....1....2....2....1....2....2....3....2

..2....3....3....3....3....1....3....1....3

..3....1....1....2....2....2....2....2....1

..2....3....3....3....3....3....3....3....3

CROSSREFS

Sequence in context: A215557 A208998 A236578 * A183471 A109677 A024122

Adjacent sequences:  A208542 A208543 A208544 * A208546 A208547 A208548

KEYWORD

nonn

AUTHOR

R. H. Hardin Feb 27 2012

STATUS

approved

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Last modified July 22 03:22 EDT 2017. Contains 289648 sequences.