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%I #10 May 01 2013 21:16:00
%S 2,2,65762,-418934878,14989881142082,-1159565898643479358,
%T 201365713271464069504802,-65359378924390295271709921438,
%U 36977332162396361445823162953505922,-33930775864190349375460255092763386069118,47994298632572575541623806754970220542333977442
%N arcsinh(sec(x)-sech(x))=2/2!*x^2+2/6!*x^6+65762/10!*x^10...
%t With[{nn=50},Take[CoefficientList[Series[ArcSinh[Sec[x]-Sech[x]],{x,0,nn}],x]Range[0,nn]!,{3,-1,4}]] (* _Harvey P. Dale_, Jan 22 2013 *)
%K sign
%O 0,1
%A Patrick Demichel (patrick.demichel(AT)hp.com)
%E More terms from _N. J. A. Sloane_, Dec 17 2011