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A168458
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a(n) = 7 + 10*floor((n-1)/2).
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1
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7, 7, 17, 17, 27, 27, 37, 37, 47, 47, 57, 57, 67, 67, 77, 77, 87, 87, 97, 97, 107, 107, 117, 117, 127, 127, 137, 137, 147, 147, 157, 157, 167, 167, 177, 177, 187, 187, 197, 197, 207, 207, 217, 217, 227, 227, 237, 237, 247, 247, 257, 257, 267, 267, 277, 277, 287
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OFFSET
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1,1
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
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FORMULA
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a(n) = 10*n - a(n-1) - 6, with n>1, a(1)=7.
G.f.: x*(7 + 3*x^2)/((1+x)*(x-1)^2). - Vincenzo Librandi, Sep 19 2013
a(n) = a(n-1) +a(n-2) -a(n-3). - Vincenzo Librandi, Sep 19 2013
From G. C. Greubel, Jul 23 2016: (Start)
a(n) = (10*n - 5*(-1)^n - 1)/2.
E.g.f.: (1/2)*(-5 + 6*exp(x) + (10*x - 1)*exp(2*x))*exp(-x). (End)
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MAPLE
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A168458:=n->7 + 10*floor((n-1)/2); seq(A168458(k), k=1..100); # Wesley Ivan Hurt, Nov 08 2013
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MATHEMATICA
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Table[7 + 10 Floor[(n - 1)/2], {n, 70}] (* or *) CoefficientList[Series[(7 + 3 x^2)/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 19 2013 *)
LinearRecurrence[{1, 1, -1}, {7, 7, 17}, 60] (* Harvey P. Dale, Apr 12 2018 *)
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PROG
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(Magma) [7+10*Floor((n-1)/2): n in [1..70]]; // Vincenzo Librandi Sep 19 2013
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CROSSREFS
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Cf. A017353.
Sequence in context: A198439 A100635 A292084 * A165138 A196395 A358380
Adjacent sequences: A168455 A168456 A168457 * A168459 A168460 A168461
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KEYWORD
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nonn,easy
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AUTHOR
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Vincenzo Librandi, Nov 26 2009
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EXTENSIONS
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New definition by Vincenzo Librandi, Sep 19 2013
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STATUS
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approved
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