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 A294971 #11 Sep 08 2022 08:46:20
%S A294971 1,9,225,11025,99225,12006225,2029052025,2029052025,586396035225,
%T A294971 211688968716225,211688968716225,111983464450883025,
%U A294971 2799586611272075625,25196279501448680625,21190071060718340405625,20363658289350325129805625
%N A294971 Denominators of the partial sums for the Catalan constant A006752: Sum_{k=0..n} ((-1)^k)/(2*k+1)^2, n >= 0.
%C A294971 The corresponding numerators are given in A294970. There details are given.
%H A294971 G. C. Greubel, <a href="/A294971/b294971.txt">Table of n, a(n) for n = 0..575</a>
%F A294971 a(n) = numerator(r(n)) with the rationals r(n) = Sum_{k=0..n} (-1)^k/(2*k+1)^2.
%F A294971 For r(n) in terms of the Hurwitz Zeta function or the trigamma function see A294970.
%e A294971 See A294970.
%t A294971 Table[Denominator[Sum[(-1)^k/(2*k+1)^2, {k,0,n}]], {n,0,20}] (* _Vaclav Kotesovec_, Nov 15 2017 *)
%o A294971 (PARI) for(n=0,20, print1(denominator(sum(k=0,n, (-1)^k/(2*k+1)^2)), ", ")) \\ _G. C. Greubel_, Aug 22 2018
%o A294971 (Magma) [Denominator((&+[(-1)^k/(2*k+1)^2: k in [0..n]])): n in [0..20]]; // _G. C. Greubel_, Aug 22 2018
%Y A294971 Cf. A006752, A294970.
%K A294971 nonn,frac,easy
%O A294971 0,2
%A A294971 _Wolfdieter Lang_, Nov 15 2017