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 A096721 #10 Nov 19 2016 03:12:31
%S A096721 0,0,0,-1,13,-2329,3749,-1405132357,41223659,-3230487913,
%T A096721 87420689313263,-92876785811395309,6545378422138547141,
%U A096721 -76226954122169434345117,13717355610784766550119,-152042860419225571514252591,325359516347299085987218014617,-501994552683503696983628163720749,226141284010354023120430917899293
%N A096721 Numerators of terms in series expansion of arcsin(arctan(x)) - arctan(arcsin(x)).
%H A096721 G. C. Greubel, <a href="/A096721/b096721.txt">Table of n, a(n) for n = 0..200</a>
%e A096721 arcsin(arctan(x)) - arctan(arcsin(x)) = -1/30*x^7 + 13/756*x^9 - 2329/75600*x^11 + 3749/199584*x^13 - 1405132357/54486432000*x^15 + ...
%t A096721 With[{nn=40},Numerator[Take[CoefficientList[Series[ArcSin[ArcTan[x]] - ArcTan[ArcSin[x]],{x,0,nn}],x],{2,-1,2}]]] (* _Harvey P. Dale_, Dec 07 2011 *)
%Y A096721 Cf. A096722, A096717, A096718, A096664, A096671, A096712, A096716, A045688, A045689, A096719, A096720.
%K A096721 sign,frac
%O A096721 0,5
%A A096721 _N. J. A. Sloane_, Aug 15 2004