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A012154
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sech(tan(tan(x))) = 1-1/2!*x^2-11/4!*x^4-253/6!*x^6-9015/8!*x^8 ... .
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0
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1, -1, -11, -253, -9015, -362009, 2294909, 7143505067, 2709263596817, 958529947538255, 359564035447469189, 146418020203030157779, 64393370639942123229401, 29924760789755403918019639
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OFFSET
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0,3
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LINKS
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MATHEMATICA
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With[{nn=30}, Take[CoefficientList[Series[Sech[Tan[Tan[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Sep 15 2023 *)
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CROSSREFS
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KEYWORD
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sign
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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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