A012673 Expansion of e.g.f. tanh(tanh(x)*tan(x)) (even powers only).

2, -128, 12032, 365688832, -2002811158528, -67148259011330048, 3766780331499896963072, 40680896591210190242578432, -72225295511520670153244114157568, 5916291050618669748975903952466870272, 5796354619873310706800860937786561713405952, -2149645111584536569210720304942928160515820617728

Offset

0,1

Links

Table of n, a(n) for n=0..11.

Formula

a(n) = 2 * A009823(n).

Example

2/2!*x^2-128/6!*x^6+12032/10!*x^10...

Mathematica

a[n_]:=(4n+2)!SeriesCoefficient[Tanh[ Tanh[ x ]*Tan[ x ] ], {x, 0, 4n+2}]; Array[a, 11, 0] (* Stefano Spezia, Sep 03 2025 *)

Crossrefs

Cf. A009823.

Sequence in context: A277757 A010367 A024344 * A382359 A358486 A086190

Adjacent sequences: A012670 A012671 A012672 * A012674 A012675 A012676

Keyword

sign

Author

Patrick Demichel

Extensions

a(9)-a(11) from Stefano Spezia, Sep 03 2025

Status

approved