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 A009805 #21 Jan 12 2025 12:11:13
%S A009805 1,-124,262096,-2681078464,83993259325696,-6291889632188161024,
%T A009805 963296773204704677810176,-270352239123704851078462357504,
%U A009805 128399592149905444543967414059073536,-97061880731293117665388947647693059784704,111259126741155511631646423576320132328299954176
%N A009805 Expansion of e.g.f. tanh(sinh(x)*sin(x))/2 in odd powers of x^2.
%H A009805 Andrew Howroyd, <a href="/A009805/b009805.txt">Table of n, a(n) for n = 0..100</a>
%e A009805 x^2/2! - 124*x^6/6! + 262096*x^10/10! - 2681078464*x^14/14! ...
%t A009805 Tanh[ Sinh[ x ]*Sin[ x ] ]/2 (* [ x^(4n+2) ] *)
%t A009805 With[{nn=34},Take[CoefficientList[Series[Tanh[Sinh[x]Sin[x]]/2,{x,0,nn}],x] Range[0,nn]!,{3,-1,4}]] (* _Harvey P. Dale_, May 28 2019 *)
%o A009805 (PARI) seq(n)={my(A=O(x^(4*n+2))); Vec(substpol(serlaplace( tanh(sinh(x + A)*sin(x + A))/2 )/x^2, x^4, x))} \\ _Andrew Howroyd_, Jan 12 2025
%Y A009805 Cf. A023702.
%K A009805 sign
%O A009805 0,2
%A A009805 _R. H. Hardin_
%E A009805 Extended with signs by _Olivier Gérard_, Mar 15 1997
%E A009805 a(9) onwards from _Andrew Howroyd_, Jan 12 2025