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A013453
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tan(tan(x)-tanh(x))=4/3!*x^3+544/7!*x^7+35840/9!*x^9+707584/11!*x^11...
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1
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0, 4, 0, 544, 35840, 707584, 298721280, 26768052224, 5564833464320, 1787224334270464, 379247341296680960, 181364573942845538304, 71776324876296729395200, 35085662010847230106271744
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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 * (2*n+1)! / ((1/(cos(r))^2 - 1/(cosh(r))^2) * r^(2*n+2)), where r = 1.175536528296496445322181894766544798346231323714914157798... is the root of the equation tan(r)-tanh(r) = Pi/2. - Vaclav Kotesovec, Feb 06 2015
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MATHEMATICA
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nn = 20; Table[(CoefficientList[Series[Tan[Tan[x] - Tanh[x]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 06 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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EXTENSIONS
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STATUS
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approved
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