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 A189806 #14 Jan 17 2018 03:33:24
%S A189806 1,16,64,2048,8192,262144,1048576,67108864,268435456,17179869184,
%T A189806 68719476736,2199023255552,8796093022208,281474976710656,
%U A189806 1125899906842624,144115188075855872,576460752303423488,73786976294838206464,295147905179352825856,9444732965739290427392,37778931862957161709568
%N A189806 Denominators of coefficients in the series expansion of ((2 - m) EllipticK(m) - 2 EllipticE(m))/(Pi * m).
%C A189806 This combination of elliptic functions appears in the expression for the vector potential generated by a circular loop of current. The denominators are powers of 2. The base-2 logarithm of the denominators increments in pattern related to A090739. That latter sequence begins 3,4,3,5,3,4,3,6. Add 2 to each entry; thus, 5,6,5,7,5,6,5,8. Duplicate each entry; thus, 5,5,6,6,5,5,7,7,5,5,6,6,5,5,8,8. Now insert a 2 at the beginning and between each entry; thus, 2,5,2,5,2,6,2,6,2,5,2,5,2, 7,2,7,2,5,2,5,2,6,2,6,2,5,2,5,2,8,2,8. Finally, prepend a 4; thus 4,2,5,2,5,2,6,2,6,2,5,2,5,2,7,2,7,2,5,2,5,2,6,2,6,2,5,2,5,2,8,2,8. This yields the pattern of increments in the base-2 logarithm of the denominators. See also the construction of the ruler sequence A007814.
%D A189806 J. D. Jackson, Classical Electrodynamics, John Wiley & Sons, third edition, 1999, eq.(5.37).
%H A189806 G. C. Greubel, <a href="/A189806/b189806.txt">Table of n, a(n) for n = 0..830</a>
%F A189806 a(n) is the denominator of the fraction ((2n-1)!!)^2/(2^(2n+1)*(n-1)!*(n+1)!).
%t A189806 Denominator[CoefficientList[Series[((2-m)EllipticK[m]-2EllipticE[m])/m,{m,0,20}]/Pi,m]]
%Y A189806 Cf. A189805, A090739, A007814.
%K A189806 nonn,frac
%O A189806 0,2
%A A189806 _Dan T. Abell_, Apr 28 2011