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%I #14 Nov 08 2013 09:32:22
%S 1,-1,17,-721,56993,-7232161,1344866225,-344599447921,116382225519425,
%T -50097660050713921,26773024797675332945,-17392081348966913859601,
%U 13497082647397365780254177
%N E.g.f.: sech(sin(arctan(x))) (even powers only).
%H Vincenzo Librandi, <a href="/A012029/b012029.txt">Table of n, a(n) for n = 0..50</a>
%F a(n) ~ (-1)^n * 2^(2*n+5) * n^(2*n+1/2) * (Pi^2+4)^(n-1) / (exp(2*n) * Pi^(2*n+1/2)). - _Vaclav Kotesovec_, Nov 08 2013
%e sech(sin(arctan(x))) = 1 -1/2!*x^2 +17/4!*x^4 -721/6!*x^6 +56993/8!*x^8 ...
%t With[{nn=30},Take[CoefficientList[Series[Sech[Sin[ArcTan[x]]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Oct 03 2013 *)
%K sign
%O 0,3
%A Patrick Demichel (patrick.demichel(AT)hp.com)
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