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 A296853 #6 Dec 26 2017 18:05:34
%S A296853 0,1,1,-27,-403,8345,688473,-208019,-3189211931,-162605047455,
%T A296853 28806493001105,5257860587364341,-288068264497990179,
%U A296853 -230932276247139756887,-14420179324444754436023,13944106915630111553887485,3643613240568912544562868053
%N A296853 Expansion of e.g.f. tanh(x*tan(x/2)) (even powers only).
%F A296853 a(n) = (2*n)! * [x^(2*n)] tanh(x*tan(x/2)).
%e A296853 tanh(x*tan(x/2)) = x^2/2! + x^4/4! - 27*x^6/6! - 403*x^8/8! + 8345*x^10/10! + ...
%t A296853 nmax = 16; Table[(CoefficientList[Series[Tanh[x Tan[x/2]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%Y A296853 Cf. A000182, A001469, A003721, A009817, A110501, A296839, A296841, A296842, A296854, A296856.
%K A296853 sign
%O A296853 0,4
%A A296853 _Ilya Gutkovskiy_, Dec 21 2017