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A131738
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a(0) = 0. a(n) = (n+1)*(-1)^n, n>0 .
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2
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0, -2, 3, -4, 5, -6, 7, -8, 9, -10, 11, -12, 13, -14, 15, -16, 17, -18, 19, -20, 21, -22, 23, -24, 25, -26, 27, -28, 29, -30, 31, -32, 33, -34, 35, -36, 37, -38, 39, -40, 41, -42, 43, -44, 45, -46, 47, -48, 49, -50, 51, -52, 53, -54, 55, -56, 57, -58, 59, -60, 61, -62, 63, -64, 65, -66, 67, -68, 69, -70, 71, -72, 73, -74, 75
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OFFSET
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0,2
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COMMENTS
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Also the main diagonal of A138057.
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 0..5000
Index entries for linear recurrences with constant coefficients, signature (-2,-1).
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FORMULA
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From G. C. Greubel, Nov 02 2017: (Start)
a(n) = -2*a(n-1) - a(n-2).
G.f.: -x*(x+2)/(1+x)^2.
E.g.f.: (1 - x - exp(x))*exp(-x). (End)
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MATHEMATICA
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Join[{0}, Table[(-1)^n*(n + 1), {n, 1, 50}]] (* G. C. Greubel, Nov 02 2017 *)
LinearRecurrence[{-2, -1}, {0, -2, 3}, 80] (* Harvey P. Dale, Dec 03 2022 *)
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PROG
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(PARI) a(n)=if(n, (n+1)*(-1)^n, 0) \\ Charles R Greathouse IV, Sep 01 2015
(Magma) [0] cat [(-1)^n*(n+1): n in [1..50]]; // G. C. Greubel, Nov 02 2017
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CROSSREFS
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Cf. A105811.
Sequence in context: A114142 A020725 A119972 * A199969 A303502 A000027
Adjacent sequences: A131735 A131736 A131737 * A131739 A131740 A131741
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KEYWORD
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sign,easy
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AUTHOR
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Paul Curtz, Sep 19 2007
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EXTENSIONS
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Edited by R. J. Mathar, Jul 07 2008
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STATUS
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approved
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