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%I #21 Aug 01 2022 19:03:38
%S 1,0,0,160,0,261120,19712000,1538068480,557613056000,72297758064640,
%T 26395258519552000,9009548633571328000,3030117499561574400000,
%U 1720760994441294994472960,838542041341593366036480000,545911029456375473017632849920,403794537898256808435202916352000
%N Expansion of e.g.f. sec(tan(x) - tanh(x)) (even-indexed coefficients only).
%F a(n) = (2n)! * [x^(2n)] sec(tan(x)-tanh(x)). - _Alois P. Heinz_, Aug 01 2022
%e sec(tan(x)-tanh(x)) = 1 + 160/6!*x^6 + 261120/10!*x^10 + 19712000/12!*x^12 ... .
%p a:= n-> (t-> t!*coeff(series(sec(tan(x)-tanh(x)), x, t+1), x, t))(2*n):
%p seq(a(n), n=0..16); # _Alois P. Heinz_, Aug 01 2022
%K nonn
%O 0,4
%A Patrick Demichel (patrick.demichel(AT)hp.com)
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