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A155769
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a(n) = 2n^2 + 2n - 41.
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4
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-41, -37, -29, -17, -1, 19, 43, 71, 103, 139, 179, 223, 271, 323, 379, 439, 503, 571, 643, 719, 799, 883, 971, 1063, 1159, 1259, 1363, 1471, 1583, 1699, 1819, 1943, 2071, 2203, 2339, 2479, 2623, 2771, 2923, 3079, 3239, 3403, 3571, 3743, 3919, 4099, 4283
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OFFSET
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0,1
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LINKS
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FORMULA
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Sum_{n>=0} 1/a(n) = tan(sqrt(83)*Pi/2)*Pi/(2*sqrt(83)). - Amiram Eldar, Feb 25 2023
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MATHEMATICA
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CoefficientList[Series[(-41+86x-41x^2)/(1-x)^3, {x, 0, 50}], x] (* Vincenzo Librandi, Feb 29 2012 *)
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PROG
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(Magma) I:=[-41, -37, -29]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 29 2012
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CROSSREFS
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KEYWORD
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sign,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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