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 A009119 #20 Jul 26 2018 03:43:03
%S A009119 1,-1,13,-301,11705,-698521,59340997,-6782462597,1000434618609,
%T A009119 -184576848771889,41577074746699261,-11216502744649033437,
%U A009119 3567416307426404300713,-1320192785381894987925961,562163981454375064332029365,-272809563505907130928868599861
%N A009119 Expansion of e.g.f. cos(x/cosh(x)) (even powers only).
%H A009119 G. C. Greubel, <a href="/A009119/b009119.txt">Table of n, a(n) for n = 0..238</a>
%F A009119 a(n) = 2*Sum_{k=1..n-1} binomial(2*n,2*k)*Sum_{j=0..(n-k)} binomial(k+j-1,j)*4^(n-k-j)*Sum_{i=0..j} (i-j)^(2*n-2*k)*binomial(2*j,i)*(-1)^(k+j-i) +(-1)^n. - _Vladimir Kruchinin_, Jun 16 2011
%t A009119 With[{nn=30},Take[CoefficientList[Series[Cos[x/Cosh[x]],{x,0,nn}],x] Range[ 0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Jul 07 2017 *)
%o A009119 (Maxima)
%o A009119 a(n):=2*sum(binomial(2*n,2*k)*sum(binomial(k+j-1,j)*4^(n-k-j)*sum((i-j)^(2*n-2*k)*binomial(2*j,i)*(-1)^(k+j-i),i,0,j),j,0,(n-k)),k,1,n-1)+(-1)^n; /* _Vladimir Kruchinin_, Jun 16 2011 */
%o A009119 (PARI) x='x+O('x^50); v=Vec(serlaplace(cos(x/cosh(x)))); vector(#v\2,n,v[2*n-1]) \\ _G. C. Greubel_, Jul 26 2018
%K A009119 sign
%O A009119 0,3
%A A009119 _R. H. Hardin_
%E A009119 Extended with signs by _Olivier Gérard_, Mar 15 1997