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 A092266 #12 Sep 27 2019 12:13:32
%S A092266 1,4,4,16,36,144,400,1600,4900,19600,63504,254016,853776,3415104,
%T A092266 11778624,47114496,165636900,662547600,2363904400,9455617600,
%U A092266 34134779536,136539118144,497634306624,1990537226496,7312459672336
%N A092266 Expansion of (1+4x)/AGM(1+4x,1-4x) where AGM denotes the arithmetic-geometric mean.
%F A092266 G.f.: (1+4x)/AGM(1+4x, 1-4x) where AGM(x, y) is the arithmetic-geometric mean of Gauss and Legendre.
%F A092266 a(n) = A063886(n)^2.
%F A092266 a(2n) = A002894(n); a(2n+1) = 4*a(2n).
%F A092266 a(n) ~ 2^(2*n + 1) / (Pi*n). - _Vaclav Kotesovec_, Sep 27 2019
%t A092266 CoefficientList[Series[2*(1 + 4*x)*EllipticK[1 - (1 + 4*x)^2/(1 - 4*x)^2] / (Pi*(1 - 4*x)), {x, 0, 30}], x] (* _Vaclav Kotesovec_, Sep 27 2019 *)
%o A092266 (PARI) a(n)=((n==0)+2*binomial(n-1,(n-1)\2))^2;
%o A092266 (PARI) Vec( 1/agm(1,(1-4*x)/(1+4*x)+O(x^66)) ) \\ _Joerg Arndt_, Aug 14 2013
%K A092266 nonn
%O A092266 0,2
%A A092266 _Michael Somos_, Feb 16 2004