A012388 arcsin(tan(x)*tan(x))=2/2!*x^2+16/4!*x^4+392/6!*x^6+21376/8!*x^8...

0, 2, 16, 392, 21376, 2117792, 333550336, 76433892992, 23981418704896, 9862199971860992, 5144452992189485056, 3317894031273853601792, 2591931617534673513250816, 2411532576645611695219515392

Offset: 0

Author

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

Keywords

• nonn

Programs

Mathematica

nn = 20; Table[(CoefficientList[Series[ArcSin[Tan[x]^2], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Feb 08 2015 *)

Formula

a(n) ~ 2^(4*n-1) * (2*n)! / (n^(3/2) * Pi^(2*n)). - Vaclav Kotesovec, Feb 08 2015

Extensions

a(0)=0 prepended by Vaclav Kotesovec, Feb 08 2015