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A161365
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a(n) = 3/2 + 5*n - 5*(-1)^n/2.
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1
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9, 9, 19, 19, 29, 29, 39, 39, 49, 49, 59, 59, 69, 69, 79, 79, 89, 89, 99, 99, 109, 109, 119, 119, 129, 129, 139, 139, 149, 149, 159, 159, 169, 169, 179, 179, 189, 189, 199, 199, 209, 209, 219, 219, 229, 229, 239, 239, 249, 249, 259, 259, 269, 269, 279, 279, 289
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 10*n - a(n-1) - 2, n > 1.
G.f.: x*(9+x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Jan 05 2011
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MATHEMATICA
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PROG
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(Magma) I:=[9, 9, 19]; [n le 3 select I[n] else Self(n-1)+Self(n-2)-Self(n-3): n in [1..60]]; // Vincenzo Librandi, Mar 02 2012
(PARI) for(n=1, 60, print1(3/2+5*n-5*(-1)^n/2", ")); \\ Vincenzo Librandi, Mar 02 2012
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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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