# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a012849
Showing 1-1 of 1

%I A012849 #8 Feb 05 2015 15:41:12
%S A012849 1,7,193,13319,1721281,357281351,108706678273,45591739883975,
%T A012849 25211971076762753,17775279702237604231,15562493015528998511681,
%U A012849 16565188691481564795512967,21067308092979783990029042241
%N A012849 arctanh(sec(x)*arctanh(x))=x+7/3!*x^3+193/5!*x^5+13319/7!*x^7...
%F A012849 a(n) ~ (2*n)! / r^(2*n+1), where r = 0.6588155299144662008044917663989656738607... is the root of the equation sec(r)*arctanh(r) = 1. - _Vaclav Kotesovec_, Feb 05 2015
%t A012849 With[{nn=30},Take[CoefficientList[Series[ArcTanh[Sec[x]ArcTanh[x]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Jan 03 2014 *)
%K A012849 nonn
%O A012849 0,2
%A A012849 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A012849 Definition clarified by _Harvey P. Dale_, Jan 03 2014

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE