A012165 - OEIS

%I #9 Feb 03 2015 08:44:40

%S 1,-1,1,-57,4513,-362737,43685409,-7472568937,1694762362561,

%T -492370173816033,178467092014537921,-78960125273223620761,

%U 41880334808869380979041,-26232480244560931030777297

%N tanh(tan(arcsinh(x)))=x-1/3!*x^3+1/5!*x^5-57/7!*x^7+4513/9!*x^9...

%H Vaclav Kotesovec, <a href="/A012165/b012165.txt">Table of n, a(n) for n = 0..200</a>

%F a(n) ~ (-1)^n * c * (2*n)! / sqrt(n), where c = 0.2423459676113260058762976897... . - _Vaclav Kotesovec_, Feb 03 2015

%t With[{nn=30},Take[CoefficientList[Series[Tanh[Tan[ArcSinh[x]]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Jun 19 2013 *)

%K sign

%O 0,4

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