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 A134805 #15 Jan 05 2025 19:51:38
%S A134805 1,2,24,360,2016,16800,237600,151351200,605404800,30875644800,
%T A134805 53330659200,6453009763200,11416863427200,1929449919196800,
%U A134805 1929449919196800,93256746094512000,680225677395264000,196585220767231296000,93119315100267456000,1243794691794272409792000
%N A134805 Denominator of Sum_{i=1..n} 1/(i^2*binomial(2*i,i)).
%C A134805 For this sum times 2/3 see A130549/A130550 with offset 1.
%H A134805 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 A134805 Sum_{i >= 1} 1/(i^2*binomial(2*i, i)) = Pi^2/18.
%e A134805 0, 1/2, 13/24, 197/360, 1105/2016, 9211/16800, 130277/237600, 82987349/151351200, ...
%p A134805 seq(denom(add(1/(k^2*binomial(2*k, k)), k = 1 .. n)), n = 0 .. 19); # _Peter Bala_, Mar 03 2015
%t A134805 Join[{1},Denominator[Accumulate[Table[1/(n^2 Binomial[2n,n]),{n,20}]]]] (* _Harvey P. Dale_, Jun 07 2021 *)
%o A134805 (PARI) a(n) = denominator(sum(i=1, n, 1/(i^2*binomial(2*i, i)))); \\ _Michel Marcus_, Mar 10 2016
%Y A134805 For numerators see A130549, n>=1.
%K A134805 nonn,frac
%O A134805 0,2
%A A134805 _Wolfdieter Lang_ and _N. J. A. Sloane_, Oct 13 2008