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 A352465 #5 Mar 18 2022 00:12:23
%S A352465 1,1,19,1576,356035,172499176,154989443170,234120771123513,
%T A352465 553941959716031715,1945912976888526218512,9731900583801946493234794,
%U A352465 66990924607889809703423378253,617312916540194845307221190273098,7439659538258619452171059589120614701
%N A352465 a(0) = 1; a(n) = (1/n) * Sum_{k=1..n} binomial(2*n,2*k)^2 * k * a(n-k).
%F A352465 Sum_{n>=0} a(n) * x^(2*n) / (2*n)!^2 = exp( Sum_{n>=1} x^(2*n) / (2*n)!^2 ).
%F A352465 Sum_{n>=0} a(n) * x^(2*n) / (2*n)!^2 = exp( (BesselI(0,2*sqrt(x)) + BesselJ(0,2*sqrt(x))) / 2 - 1 ).
%t A352465 a[0] = 1; a[n_] := a[n] = (1/n) Sum[Binomial[2 n, 2 k]^2 k a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 13}]
%t A352465 nmax = 26; Take[CoefficientList[Series[Exp[Sum[x^(2 k)/(2 k)!^2, {k, 1, nmax}]], {x, 0, nmax}], x] Range[0, nmax]!^2, {1, -1, 2}]
%Y A352465 Cf. A005046, A023998, A346220, A352466.
%K A352465 nonn
%O A352465 0,3
%A A352465 _Ilya Gutkovskiy_, Mar 17 2022