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 A335090 #21 Apr 29 2021 04:34:00
%S A335090 0,1,34,1891,164196,20760741,3616621254,832001250375,244557191709000,
%T A335090 89472598178279625,39886085958271670250,21288783013213520392875,
%U A335090 13405493416599700058947500,9835107221539462476348118125,8316889511005794888839427108750,8030850428074789829954674314399375
%N A335090 a(n) = ((2*n+1)!!)^2 * (Sum_{k=1..n} 1/(2*k+1)^2).
%F A335090 a(n) = (8*n^2+2) * a(n-1) - (2*n-1)^4 * a(n-2) for n>1.
%F A335090 a(n) ~ (Pi^2/8 - 1) * 2^(2*n + 3) * n^(2*n + 2) / exp(2*n). - _Vaclav Kotesovec_, Sep 25 2020
%t A335090 a[n_] := ((2*n + 1)!!)^2 * Sum[1/(2*k + 1)^2, {k, 1, n}]; Array[a, 16, 0] (* _Amiram Eldar_, Apr 29 2021 *)
%o A335090 (PARI) {a(n) = prod(k=1, n, 2*k+1)^2*sum(k=1, n, 1/(2*k+1)^2)}
%o A335090 (PARI) {a(n) = if(n<2, n, (8*n^2+2)*a(n-1)-(2*n-1)^4*a(n-2))}
%Y A335090 Column k=2 of A335095.
%Y A335090 Cf. A001824, A334670, A335091, A335092.
%K A335090 nonn
%O A335090 0,3
%A A335090 _Seiichi Manyama_, Sep 11 2020