This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A213069 #17 Aug 19 2018 02:59:40
%S A213069 0,-1,3,-1,-77,-13921,791043,23892959,-3518362637,-801110007361,
%T A213069 149920222346883,24069808471917119,-7334638751184472397,
%U A213069 -2673575321959933341601,1059696929013386749787523,413637485668406346391368479
%N A213069 Expansion of e.g.f. arcsinh(cos(x)*sech(x)), even powers only.
%C A213069 This function is even, with constant term arcsinh(1) = 0.881373587019543...
%H A213069 Vincenzo Librandi, <a href="/A213069/b213069.txt">Table of n, a(n) for n = 0..100</a>
%F A213069 E.g.f.: (arcsinh(cos(x)*sech(x))-arcsinh(1))/sqrt(2).
%e A213069 (arcsinh(cos(x)*sech(x))-arcsinh(1))/sqrt(2) = -x^2/2 + 3*x^4/4! - x^6/6! - 77*x^8/8! + ...
%t A213069 Part[#, Range[1, Length[#], 2]] &@(Array[#! &, Length[#], 0]*#) &@ CoefficientList[Series[(ArcSinh[Cos[x]*Sech[x]] - ArcSinh[1])/Sqrt[2], {x, 0, 30}], x] // ExpandAll
%t A213069 With[{nn=30},Take[CoefficientList[Series[(ArcSinh[Cos[x]Sech[x]]-ArcSinh[ 1])/ Sqrt[2],{x,0,nn}],x]Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Mar 24 2013 *)
%Y A213069 Cf. A213066, A213067, A213068.
%K A213069 sign
%O A213069 0,3
%A A213069 _Olivier Gérard_, Jun 04 2012