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27, 36, 81, 72, 135, 108, 189, 144, 243, 180, 297, 216, 351, 252, 405, 288, 459, 324, 513, 360, 567, 396, 621, 432, 675, 468, 729, 504, 783, 540, 837, 576, 891, 612, 945, 648, 999, 684, 1053, 720, 1107
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OFFSET
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0,1
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COMMENTS
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All terms are multiples of 9.
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LINKS
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FORMULA
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G.f.: 9*(3+4*x+3*x^2)/((x-1)^2*(1+x)^2).
a(n) = 45*(n+1)/2 + 9*(-1)^n*(n+1)/2. (End)
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MATHEMATICA
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LinearRecurrence[{0, 2, 0, -1}, {27, 36, 81, 72}, 50] (* Harvey P. Dale, Nov 07 2019 *)
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PROG
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(PARI) a(n) = 45*(n+1)/2 + 9*(-1)^n*(n+1)/2 \\ Jianing Song, Feb 04 2019
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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