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 A013521 #15 Nov 12 2016 08:08:19
%S A013521 1,-1,-7,-97,-2063,-17803,-250781,166831871,43685848289,447550424579,
%T A013521 84677077231169,11657476758734011,28924058075775365981,
%U A013521 44287070229737735633567,305190813989360271816409
%N A013521 Numerator of [x^(2n)] in the Taylor expansion cos(cosec(x)-cot(x))= 1-x^2/8 -7*x^4/384 -97*x^6/46080 -2063*x^8/10321920 -17803*x^10/1238630400 -....
%C A013521 The e.g.f of x/2, cos(cosec(x)-cot(x)) = 1 -1*x^2/(2^2*2!) -7*x^4/(2^4*4!) -97*x^6/(2^6*6!) -2063*x^8/(2^8*8!) -..., is apparently covered by A003710.
%H A013521 G. C. Greubel, <a href="/A013521/b013521.txt">Table of n, a(n) for n = 0..125</a>
%t A013521 Numerator[Take[CoefficientList[Series[Cos[Csc[x] - Cot[x]], {x, 0, 25}], x], {1, -1, 2}]] (* _G. C. Greubel_, Nov 12 2016 *)
%K A013521 sign,frac
%O A013521 0,3
%A A013521 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A013521 Name edited by _R. J. Mathar_, Dec 19 2011