A013455 - OEIS

A013455

Expansion of e.g.f. sec(tan(x) - tanh(x)) (even-indexed coefficients only).

1, 0, 0, 160, 0, 261120, 19712000, 1538068480, 557613056000, 72297758064640, 26395258519552000, 9009548633571328000, 3030117499561574400000, 1720760994441294994472960, 838542041341593366036480000, 545911029456375473017632849920, 403794537898256808435202916352000

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..16.

FORMULA

a(n) = (2n)! * [x^(2n)] sec(tan(x)-tanh(x)). - Alois P. Heinz, Aug 01 2022

EXAMPLE

sec(tan(x)-tanh(x)) = 1 + 160/6!*x^6 + 261120/10!*x^10 + 19712000/12!*x^12 ... .

MAPLE

a:= n-> (t-> t!*coeff(series(sec(tan(x)-tanh(x)), x, t+1), x, t))(2*n):

seq(a(n), n=0..16); # Alois P. Heinz, Aug 01 2022

CROSSREFS

Sequence in context: A213695 A224430 A013454 * A013465 A013466 A376899

Adjacent sequences: A013452 A013453 A013454 * A013456 A013457 A013458

KEYWORD

nonn

AUTHOR

Patrick Demichel (patrick.demichel(AT)hp.com)

STATUS

approved