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A007455
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Number of subsequences of [ 1,...,n ] in which each odd number has an even neighbor.
(Formerly M2480)
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4
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1, 1, 3, 5, 11, 17, 39, 61, 139, 217, 495, 773, 1763, 2753, 6279, 9805, 22363, 34921, 79647, 124373, 283667, 442961, 1010295, 1577629, 3598219, 5618809, 12815247, 20011685, 45642179, 71272673, 162557031, 253841389, 578955451, 904069513
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OFFSET
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0,3
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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a(n) = 3*a(n-2) + 2*a(n-4).
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MATHEMATICA
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CoefficientList[Series[(-1-x-2 x^3)/(-1+3 x^2+2 x^4), {x, 0, 40}], x] (* Harvey P. Dale, Feb 18 2011 *)
LinearRecurrence[{0, 3, 0, 2}, {1, 1, 3, 5}, 40] (* Harvey P. Dale, Feb 10 2015 *)
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PROG
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(Haskell)
a007455_list = 1 : 1 : 3 : 5 : zipWith (+)
(map (* 2) a007455_list) (map (* 3) $ drop 2 a007455_list)
a007455 n = a007455_list !! n
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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STATUS
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approved
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