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 A012154 sech(tan(tan(x))) = 1-1/2!*x^2-11/4!*x^4-253/6!*x^6-9015/8!*x^8 ... . 0
 1, -1, -11, -253, -9015, -362009, 2294909, 7143505067, 2709263596817, 958529947538255, 359564035447469189, 146418020203030157779, 64393370639942123229401, 29924760789755403918019639 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Table of n, a(n) for n=0..13. MATHEMATICA 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 *) CROSSREFS Sequence in context: A089298 A274129 A346896 * A009055 A009067 A128683 Adjacent sequences: A012151 A012152 A012153 * A012155 A012156 A012157 KEYWORD sign AUTHOR Patrick Demichel (patrick.demichel(AT)hp.com) STATUS approved

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Last modified December 8 23:37 EST 2023. Contains 367681 sequences. (Running on oeis4.)