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A168195
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a(n) = 2*n - a(n-1) + 1 with n>1, a(1)=5.
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1
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5, 0, 7, 2, 9, 4, 11, 6, 13, 8, 15, 10, 17, 12, 19, 14, 21, 16, 23, 18, 25, 20, 27, 22, 29, 24, 31, 26, 33, 28, 35, 30, 37, 32, 39, 34, 41, 36, 43, 38, 45, 40, 47, 42, 49, 44, 51, 46, 53, 48, 55, 50, 57, 52, 59, 54, 61, 56, 63, 58, 65, 60, 67, 62, 69, 64, 71, 66, 73
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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) = a(n-1) + a(n-2) - a(n-3) = n + 1 - 3*(-1)^n.
G.f.: x*(5+2*x^2-5*x)/((1+x)*(x-1)^2). (End)
Sum_{n>=3} (-1)^n/a(n) = 23/15 - log(2). - Amiram Eldar, Feb 23 2023
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MAPLE
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MATHEMATICA
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PROG
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(Magma) I:=[5, 0, 7]; [n le 3 select I[n] else Self(n-1)+Self(n-2)-Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 27 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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STATUS
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approved
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