A012613 tan(arcsinh(x)*tan(x))=2/2!*x^2+4/4!*x^4+350/6!*x^6+7208/8!*x^8...

0, 2, 4, 350, 7208, 1278298, 79874540, 24248146806, 3094746649296, 1450703467495218, 311518889830786132, 210537148539150077966, 67821849231894539132920, 62959878878133692157576586

Offset

0,2

Links

Table of n, a(n) for n=0..13.

Formula

a(n) ~ (-1)^(n+1) * tanh(1) * 2^(2*n+1) * n^(2*n-1) / (exp(2*n) * (1+cos(Pi*tanh(1)))). - Vaclav Kotesovec, Oct 31 2013

Mathematica

Table[n!*SeriesCoefficient[Tan[ArcSinh[x]*Tan[x]], {x, 0, n}], {n, 0, 40, 2}] (* Vaclav Kotesovec, Oct 31 2013 *)

Crossrefs

Sequence in context: A012368 A009705 A012372 * A012618 A012557 A012562

Adjacent sequences: A012610 A012611 A012612 * A012614 A012615 A012616

Keyword

nonn

Author

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

Extensions

Prepended missing a(0)=0 from Vaclav Kotesovec, Oct 31 2013

Status

approved