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%I #9 Aug 15 2016 10:06:26
%S 1,1,1,25,-415,35825,-3356575,492769225,-96314333375,24701457990625,
%T -8006683308349375,3204344303824405625,-1551453429875871169375,
%U 893896220277392770140625,-604413346665043743464609375
%N E.g.f. sec(arcsinh(x)) = cosec(arccosh(x)) (even powers only).
%e sec(arcsinh(x)) = 1 + x^2/2 + x^4/4! + 25x^6/6! - 415x^8/8! +...
%e sech(arcsin(x)) = 1 - x^2/2 + x^4/4! - 25x^6/6! - 415x^8/8! -...
%t With[{nn=30},Take[CoefficientList[Series[Sec[ArcSinh[x]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Aug 15 2016 *)
%K sign
%O 0,4
%A _Ralf Stephan_, Dec 31 2004
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