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 A090855 #12 Sep 28 2019 04:49:06
%S A090855 1,4,10,24,55,127,288,640,1408,3069,6642,14281,30544,65028,137896,
%T A090855 291399,613885,1289715,2702909,5652038,11795170,24570079,51095155,
%U A090855 106092067,219972452,455493427,942031726,1946056082,4015916211
%N A090855 a(n) is the least positive integer such that the integer part of the arithmetic-geometric mean of a(n) and 1 is equal to 2^n.
%F A090855 floor( agm(a(n), 1) ) = 2^n, for n>=0.
%t A090855 Flatten[{1, Table[Ceiling[y /. FindRoot[Log[Pi/(2*EllipticK[1 - y^2])] == n*Log[2], {y, n*2^n}, MaxIterations -> 1000]], {n, 1, 50}]}] (* _Vaclav Kotesovec_, Sep 28 2019 *)
%Y A090855 Cf. A090852, A090854, A090856.
%K A090855 nonn
%O A090855 0,2
%A A090855 _Paul D. Hanna_, Dec 10 2003