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A007039
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Number of cyclic binary n-bit strings with no alternating substring of length >2.
(Formerly M0241)
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2
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2, 2, 2, 6, 12, 20, 30, 46, 74, 122, 200, 324, 522, 842, 1362, 2206, 3572, 5780, 9350, 15126, 24474, 39602, 64080, 103684, 167762, 271442, 439202, 710646, 1149852, 1860500, 3010350, 4870846, 7881194, 12752042, 20633240, 33385284, 54018522
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| John Layman (layman(AT)calvin.math.vt.edu) observes that the second differences give the sequence shifted to the right.
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REFERENCES
| Z. Agur et al., The number of fixed points of the majority rule, Discr. Math., 70 (1988), 295-302.
Moser, W. O. J.; Cyclic binary strings without long runs of like (alternating) bits. Fibonacci Quart. 31 (1993), no. 1, 2-6.
A. McLeod and W. O. J. Moser, Counting cyclic binary strings, Math. Mag., 80 (No. 1, 2007), 29-37.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (2,-1,0,1).
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FORMULA
| For n >= 5, a(n) = 2a(n-1) - a(n-2) + a(n-4) (from David W. Wilson).
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CROSSREFS
| Cf. A007040.
Sequence in context: A186507 A032306 A058756 * A025248 A101416 A098920
Adjacent sequences: A007036 A007037 A007038 * A007040 A007041 A007042
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KEYWORD
| nonn,easy,eigen
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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