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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
Sequence in context: A220598 A239926 A111920 * A166116 A173148 A142368
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 19 2017
STATUS
approved

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Last modified February 22 12:15 EST 2024. Contains 370255 sequences. (Running on oeis4.)