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A296740
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Expansion of e.g.f. sec(x*cosh(x)) (even powers only).
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6
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1, 1, 17, 481, 26529, 2355841, 304490801, 54346519137, 12784369495873, 3834072115634689, 1427927160049839185, 646549058811594306017, 349778819738933516544737, 222822626689237030117683841, 165094750167986500169166495089, 140768231241374238855897822250081
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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) = (2*n)! * [x^(2*n)] sec(x*cosh(x)).
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EXAMPLE
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sec(x*cosh(x)) = 1 + x^2/2! + 17*x^4/4! + 481*x^6/6! + 26529*x^8/8! + ...
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MATHEMATICA
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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}]
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PROG
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(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
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CROSSREFS
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Cf. A000364, A009008, A009009, A009010, A009011, A009015, A009016, A009446, A009447, A009633, A009634, A102072, A102075, A191512, A296728, A296729, A296730, A296731.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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