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Search: id:A006904
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| A006904 |
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a(n) = a(n-1)+2.a(n-2)+(-1)^n.
(Formerly M3254)
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+0
2
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| 1, 1, 4, 5, 14, 23, 52, 97, 202, 395, 800, 1589, 3190, 6367, 12748, 25481, 50978, 101939, 203896, 407773, 815566, 1631111, 3262244, 6524465, 13048954, 26097883, 52195792, 104391557
(list; graph; listen)
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OFFSET
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4,3
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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).
R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 1990, p. 327.
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FORMULA
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G.f.: (1+x+x^2 ) / (1-2x)(1+x)^2.
With offset 0: a(n) = 1/9*(7*2^n+(-1)^n*(3*n+2)); if b(1)=1, b(k) = 2*b(k-1)+(-1)^k*k, then for n>4, a(n)=b(n-4). - Benoit Cloitre (benoit7848c(AT)orange.fr), Oct 28 2002
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CROSSREFS
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Adjacent sequences: A006901 A006902 A006903 this_sequence A006905 A006906 A006907
Sequence in context: A041089 A042321 A050164 this_sequence A007084 A093862 A041375
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KEYWORD
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nonn,easy
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AUTHOR
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Simon Plouffe, N. J. A. Sloane (njas(AT)research.att.com).
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