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 A354305 #7 Apr 25 2023 15:02:15
%S A354305 1,1,4,9,192,1800,103680,529200,232243200,8230118400,1463132160000,
%T A354305 39833773056000,20858412072960000,1615657835151360000,
%U A354305 584619573580922880000,1908495817772544000000,29184209113159670169600000,3953548328298349068288000000,185476873609942457647104000000
%N A354305 a(n) is the denominator of Sum_{k=0..n} (-1)^k / (k!)^2.
%F A354305 Denominators of coefficients in expansion of BesselJ(0,2*sqrt(x)) / (1 - x).
%e A354305 1, 0, 1/4, 2/9, 43/192, 403/1800, 23213/103680, 118483/529200, 51997111/232243200, 1842647621/8230118400, ...
%t A354305 Table[Sum[(-1)^k/(k!)^2, {k, 0, n}], {n, 0, 18}] // Denominator
%t A354305 nmax = 18; CoefficientList[Series[BesselJ[0, 2 Sqrt[x]]/(1 - x), {x, 0, nmax}], x] // Denominator
%t A354305 Accumulate[Table[(-1)^k/(k!)^2,{k,0,20}]]//Denominator (* _Harvey P. Dale_, Apr 25 2023 *)
%Y A354305 Cf. A001044, A053556, A061355, A073701, A091681, A143383, A354303, A354304 (numerators).
%K A354305 nonn,frac
%O A354305 0,3
%A A354305 _Ilya Gutkovskiy_, May 23 2022