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A007481
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Number of subsequences of [ 1,...,n ] in which each even number has an odd neighbor.
(Formerly M0828)
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4
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1, 2, 3, 7, 11, 25, 39, 89, 139, 317, 495, 1129, 1763, 4021, 6279, 14321, 22363, 51005, 79647, 181657, 283667, 646981, 1010295, 2304257, 3598219, 8206733, 12815247, 29228713, 45642179, 104099605, 162557031, 370756241, 578955451, 1320467933
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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REFERENCES
| R. K. Guy and W. O. J. Moser, Numbers of subsequences without isolated odd members. Fibonacci Quarterly, 34, No. 2, 152-155 (1996).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| T. D. Noe, Table of n, a(n) for n=0..400
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FORMULA
| a(n) = 3*a(n-2) + 2*a(n-4).
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EXAMPLE
| For n=2, there are the following three subsequences of [1,2] with the desired property: empty, [1], [1,2].
For n=3, there are the following seven subsequences of [1,2,3] with the desired property: empty, [1], [3], [1,2], [2,3], [1,3], [1,2,3].
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CROSSREFS
| Cf. A007455, A007482, A007484.
Sequence in context: A128631 A092217 A191659 * A121268 A101173 A005246
Adjacent sequences: A007478 A007479 A007480 * A007482 A007483 A007484
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KEYWORD
| nonn,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from James A. Sellers (sellersj(AT)math.psu.edu), Dec 24 1999
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