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 A086891 #6 Mar 29 2015 11:58:14
%S A086891 1,4,8,64,640,2560,35840,114688,688128,13762560,14417920,346030080,
%T A086891 1799356416,2399141888,23991418880,767725404160,2372969431040,
%U A086891 5695126634496,216414812110848,221963909857280,9322484214005760
%N A086891 Denominator of 4*(Integral_{x=0..1} (1-x^2)^((2n-1)/2) dx)/Pi.
%e A086891 a(2)=4.
%t A086891 f[n_] := Denominator[ 3Simplify[ Sqrt[2]((Integrate[(1 + x^2)^((2n - 1)/2), {x, 0, 1}]) - (2n - 1)!!ArcSinh[1]/(2n)!!)]]; Table[ f[n], {n, 1, 21}] (* _Robert G. Wilson v_, Feb 27 2004 *)
%Y A086891 Cf. A076729 and A087547.
%K A086891 frac,nonn
%O A086891 1,2
%A A086891 Al Hakanson (hawkuu(AT)excite.com), Sep 18 2003
%E A086891 More terms from _Robert G. Wilson v_, Feb 27 2004