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A012798
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arctanh(sec(x)*tan(x))=x+7/3!*x^3+185/5!*x^5+12367/7!*x^7...
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0
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1, 7, 185, 12367, 1558865, 316097527, 94003171145, 38543705698687, 20840298552277025, 14366953364916735847, 12299504390976449116505, 12801737583190675819689007, 15920156445351352463114729585
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) ~ (2*n)! / (arctan(sqrt((sqrt(5)-1)/2)))^(2*n+1). - Vaclav Kotesovec, Feb 05 2015
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MATHEMATICA
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nn = 20; Table[(CoefficientList[Series[ArcTanh[Sec[x]*Tan[x]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 05 2015 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Patrick Demichel (patrick.demichel(AT)hp.com)
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STATUS
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approved
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