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A024265
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Expansion of tan(tan(x) * x)/2.
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2
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0, 1, 4, 168, 7808, 725120, 92516352, 16783492096, 3985986666496, 1212492098764800, 457766291434373120, 210284967226818953216, 115422873756041723510784, 74614491201111668354449408
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) ~ c * d^n * n^(2*n + 1/2) / exp(2*n), where d = 3.9786913954409425781217887822690623430980810... is the root of the equation tan(2/sqrt(d)) = Pi*sqrt(d)/4 and c = 0.7028591997322... - Vaclav Kotesovec, Dec 21 2017
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MATHEMATICA
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With[{nn=30}, Take[CoefficientList[Series[(Tan[Tan[x]*x])/2, {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Nov 03 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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EXTENSIONS
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Extended and signs tested 03/97.
Definition clarified and prior Mathematica program replaced by Harvey P. Dale, Nov 03 2015
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STATUS
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approved
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