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 A085457 #13 Feb 04 2023 10:18:39
%S A085457 1,-6,48,-438,4206,-41586,418980,-4277130,44089320,-457891170,
%T A085457 4783741248,-50218890738,529300238574,-5597562756894,59366869030668,
%U A085457 -631200956847558,6725615443683870,-71800018913609970,767806202604650880,-8223081959016322530,88187484604146004506
%N A085457 Sum_{i=0..n} Sum_{j=0..i} a(j) * a(i-j) = (-11)^n.
%H A085457 Seiichi Manyama, <a href="/A085457/b085457.txt">Table of n, a(n) for n = 0..960</a>
%F A085457 G.f.: A(x)=Sqrt((1-x)/(1+11x)).
%F A085457 From _Seiichi Manyama_, Feb 03 2023: (Start)
%F A085457 a(n) = Sum_{k=0..n} (-3)^k * binomial(n-1,n-k) * binomial(2*k,k).
%F A085457 n*a(n) = -2*(5*n-2)*a(n-1) + 11*(n-2)*a(n-2). (End)
%t A085457 CoefficientList[Series[Sqrt[(1-x)/(1+11 x)], {x, 0, 20}], x]
%o A085457 (PARI) a(n) = sum(k=0, n, (-3)^k*binomial(n-1, n-k)*binomial(2*k, k)); \\ _Seiichi Manyama_, Feb 03 2023
%Y A085457 Cf. A085455, A085456.
%K A085457 easy,sign
%O A085457 0,2
%A A085457 Mario Catalani (mario.catalani(AT)unito.it), Jul 01 2003