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%I #13 Jun 22 2015 22:30:41
%S 0,1,-1,3,-10,65,-376,2723,-22800,226785,-2467456,29857443,-397200640,
%T 5785047905,-91090625536,1544546456963,-28057896929280,
%U 543833037679425,-11198060484591616,244141035610073283,-5618437516698910720
%N Expansion of log(1+tanh(x)/cos(x)).
%F a(n) ~ (n-1)! * (-1)^(n+1) / r^n, where r = 0.825607669071161851569946... is the root of the equation cos(r) = tanh(r). - _Vaclav Kotesovec_, Jan 24 2015
%t Log[ 1+Tanh[ x ]/Cos[ x ] ]
%t CoefficientList[Series[Log[1 + Sec[x]*Tanh[x]], {x, 0, 20}], x] * Range[0, 20]! (* _Vaclav Kotesovec_, Jan 24 2015 *)
%K sign,easy
%O 0,4
%A _R. H. Hardin_
%E Extended with signs by _Olivier Gérard_, Mar 15 1997