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A013455
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Expansion of e.g.f. sec(tan(x) - tanh(x)) (even-indexed coefficients only).
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0
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1, 0, 0, 160, 0, 261120, 19712000, 1538068480, 557613056000, 72297758064640, 26395258519552000, 9009548633571328000, 3030117499561574400000, 1720760994441294994472960, 838542041341593366036480000, 545911029456375473017632849920, 403794537898256808435202916352000
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) = (2n)! * [x^(2n)] sec(tan(x)-tanh(x)). - Alois P. Heinz, Aug 01 2022
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EXAMPLE
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sec(tan(x)-tanh(x)) = 1 + 160/6!*x^6 + 261120/10!*x^10 + 19712000/12!*x^12 ... .
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MAPLE
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a:= n-> (t-> t!*coeff(series(sec(tan(x)-tanh(x)), x, t+1), x, t))(2*n):
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Patrick Demichel (patrick.demichel(AT)hp.com)
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STATUS
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approved
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