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 A012457 #10 Apr 04 2016 23:19:17
%S A012457 2,-16,248,-3456,-406368,123982080,-31807263360,9173875200000,
%T A012457 -3114459024453120,1251070155460915200,-591321674803999426560,
%U A012457 326012628782956574638080,-207713640106463567695994880
%N A012457 sin(arctan(x)^2)=2/2!*x^2-16/4!*x^4+248/6!*x^6-3456/8!*x^8...
%H A012457 Robert Israel, <a href="/A012457/b012457.txt">Table of n, a(n) for n = 0..223</a>
%F A012457 Sum_{n>=0} a(n) x^(2*n+2)/(2*n+2)! = sin(arctan(x)^2). - _Robert Israel_, Apr 04 2016
%p A012457 S:= series(g,x,52):
%p A012457 seq(coeff(S,x,2*j)*(2*j)!,j=1..25); # _Robert Israel_, Apr 04 2016
%t A012457 With[{nn=30},Take[CoefficientList[Series[Sin[ArcTan[x]^2],{x,0,nn}],x] Range[0,nn]!,{3,-1,2}]] (* _Harvey P. Dale_, Aug 20 2014 *)
%K A012457 sign
%O A012457 0,1
%A A012457 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A012457 Definition clarified by _Harvey P. Dale_, Aug 20 2014