A012173 - OEIS

%I #6 Jan 15 2015 17:00:39

%S 1,-1,5,-13,-1751,132871,-6935699,5067579,89435340497,-21076246089073,

%T 3055142025663317,13219661379785475,-235907327725301640967,

%U 116095997487821991940759,-33017130566183943274793027,-532247345346868679322284213,8810833241719412871344351850401

%N sech(tan(tanh(x)))=1-1/2!*x^2+5/4!*x^4-13/6!*x^6-1751/8!*x^8...

%t With[{nn=40},Take[CoefficientList[Series[Sech[Tan[Tanh[x]]],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Jan 15 2015 *)

%K sign

%O 0,3

%A Patrick Demichel (patrick.demichel(AT)hp.com)

%E More terms from _Harvey P. Dale_, Jan 15 2015