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 A296743 Expansion of e.g.f. arctanh(x*sec(x)) (odd powers only). 3
 1, 5, 109, 5977, 612729, 100954061, 24395453861, 8128143367905, 3571195811862385, 2000535014776893973, 1391684597704875555165, 1177047158822263838854889, 1189444022487013498606939625, 1415364934488337503351305867997, 1958850511524588636608881908473749 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Table of n, a(n) for n=0..14. FORMULA a(n) = (2*n+1)! * [x^(2*n+1)] arctanh(x*sec(x)). EXAMPLE arctanh(x*sec(x)) = x/1! + 5*x^3/3! + 109*x^5/5! + 5977*x^7/7! + 612729*x^9/9! + ... MATHEMATICA nmax = 15; Table[(CoefficientList[Series[ArcTanh[x Sec[x]], {x, 0, 2 nmax + 1}], x] Range[0, 2 nmax + 1]!)[[n]], {n, 2, 2 nmax, 2}] PROG (PARI) first(n) = x='x+O('x^(2*n)); vecextract(Vec(serlaplace(atanh(x/cos(x)))), (4^n - 1)/3) \\ Iain Fox, Dec 19 2017 CROSSREFS Cf. A003700, A009118, A009119, A009562, A009563, A009765, A009843, A010050, A102075, A191003, A296465, A296467, A296741, A296742. Sequence in context: A012122 A012091 A322896 * A358781 A188457 A245106 Adjacent sequences: A296740 A296741 A296742 * A296744 A296745 A296746 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Dec 19 2017 STATUS approved

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Last modified May 31 11:21 EDT 2023. Contains 363066 sequences. (Running on oeis4.)