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 A012391 #10 Nov 28 2015 13:12:50
%S A012391 0,2,16,152,-5504,-865888,-49313024,10192998272,4634262163456,
%T A012391 729893872005632,-280859292338008064,-286057930617679095808,
%U A012391 -94104910901654903619584,51677977224364973979901952
%N A012391 arcsinh(tan(x)*tan(x))=2/2!*x^2+16/4!*x^4+152/6!*x^6-5504/8!*x^8...
%H A012391 Vaclav Kotesovec, <a href="/A012391/b012391.txt">Table of n, a(n) for n = 0..220</a>
%t A012391 With[{nn=30},Take[CoefficientList[Series[ArcSinh[Tan[x]^2],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Dec 14 2014 *)
%K A012391 sign
%O A012391 0,2
%A A012391 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A012391 Prepended a(0)=0 by _Vaclav Kotesovec_, Nov 28 2015