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 A296740 Expansion of e.g.f. sec(x*cosh(x)) (even powers only). 6
 1, 1, 17, 481, 26529, 2355841, 304490801, 54346519137, 12784369495873, 3834072115634689, 1427927160049839185, 646549058811594306017, 349778819738933516544737, 222822626689237030117683841, 165094750167986500169166495089, 140768231241374238855897822250081 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = (2*n)! * [x^(2*n)] sec(x*cosh(x)). EXAMPLE sec(x*cosh(x)) = 1 + x^2/2! + 17*x^4/4! + 481*x^6/6! + 26529*x^8/8! + ... MATHEMATICA nmax = 15; Table[(CoefficientList[Series[Sec[x Cosh[x]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}] PROG (PARI) first(n) = x='x+O('x^(2*n-2)); vecextract(Vec(serlaplace(1/cos(x*cosh(x)))), (4^n - 1)/3) \\ Iain Fox, Dec 19 2017 CROSSREFS Cf. A000364, A009008, A009009, A009010, A009011, A009015, A009016, A009446, A009447, A009633, A009634, A102072, A102075, A191512, A296728, A296729, A296730, A296731. Sequence in context: A220598 A239926 A111920 * A166116 A173148 A142368 Adjacent sequences:  A296737 A296738 A296739 * A296741 A296742 A296743 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Dec 19 2017 STATUS approved

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Last modified August 18 04:50 EDT 2019. Contains 326072 sequences. (Running on oeis4.)