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 A130550 #15 Jan 05 2025 19:51:38
%S A130550 1,12,180,1008,8400,118800,75675600,302702400,15437822400,26665329600,
%T A130550 3226504881600,5708431713600,964724959598400,964724959598400,
%U A130550 46628373047256000,340112838697632000,98292610383615648000
%N A130550 Denominators of partial sums for a series for 2*Zeta(2)/3 = (Pi^2)/9.
%C A130550 Numerators are given in A130549.
%C A130550 For the rationals r(n):= 2*sum(1/(j^2*binomial(2*j,j)),j=1..n), n>=1, the van der Poorten reference and a W. Lang link see A130551.
%H A130550 C. Elsner, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Papers1/43-1/paper43-1-5.pdf">On recurrence formulas for sums involving binomial coefficients</a>, Fib. Q., 43,1 (2005), 31-45.
%F A130550 a(n) = denominator(r(n)), n>=1.
%F A130550 Denominator of 2*Sum_{i=1..n} 1/(i^2*C(2*i,i)). - _Wolfdieter Lang_, Oct 07 2008, corrected by _Vaclav Kotesovec_, Mar 10 2016
%t A130550 Table[2*Sum[1/(i^2*Binomial[2*i, i]), {i, 1, n}], {n, 1, 20}] // Denominator (* _Vaclav Kotesovec_, Mar 10 2016 *)
%t A130550 (2Accumulate[Table[1/(n^2 Binomial[2n,n]),{n,20}]])//Denominator (* _Harvey P. Dale_, Jan 27 2019 *)
%o A130550 (PARI) a(n) = denominator(2*sum(i=1, n, 1/(i^2*binomial(2*i, i)))); \\ _Michel Marcus_, Mar 10 2016
%Y A130550 Cf. A112099, A112100, A112102, A112103, A130549.
%K A130550 nonn,frac,easy
%O A130550 1,2
%A A130550 _Wolfdieter Lang_, Jul 13 2007