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 A335091 #23 Apr 29 2021 04:34:13
%S A335091 0,1,152,55511,41625144,56246975289,124697847089808,
%T A335091 423322997436687375,2088114588247920714000,14363296872939657999716625,
%U A335091 133299155158711610547152961000,1624450039177408057102079622846375,25413656551949715361011431877529125000,500711137690193661025654228810320074015625
%N A335091 a(n) = ((2*n+1)!!)^3 * (Sum_{k=1..n} 1/(2*k+1)^3).
%F A335091 a(n) = ((2*n-1)^3+(2*n+1)^3) * a(n-1) - (2*n-1)^6 * a(n-2) for n>1.
%F A335091 a(n) ~ (7*zeta(3)/8 - 1) * 2^(3*n + 9/2) * n^(3*n + 3) / exp(3*n). - _Vaclav Kotesovec_, Sep 25 2020
%t A335091 a[n_] := ((2*n + 1)!!)^3 * Sum[1/(2*k + 1)^3, {k, 1, n}]; Array[a, 14, 0] (* _Amiram Eldar_, Apr 29 2021 *)
%o A335091 (PARI) {a(n) = prod(k=1, n, 2*k+1)^3*sum(k=1, n, 1/(2*k+1)^3)}
%o A335091 (PARI) {a(n) = if(n<2, n, ((2*n-1)^3+(2*n+1)^3)*a(n-1)-(2*n-1)^6*a(n-2))}
%Y A335091 Column k=3 of A335095.
%Y A335091 Cf. A271636, A291585, A334670, A335090, A335092.
%K A335091 nonn
%O A335091 0,3
%A A335091 _Seiichi Manyama_, Sep 11 2020