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 A296856 #4 Dec 26 2017 18:05:51
%S A296856 1,0,3,15,224,4545,126753,4626076,213703095,12167727543,835893746300,
%T A296856 68091766034061,6483302813035857,712860388963255000,
%U A296856 89585739948801890619,12753524767335858733935,2040804997678590563632568,364567987004433619078313961
%N A296856 Expansion of e.g.f. cosh(x*tan(x/2)) (even powers only).
%F A296856 a(n) = (2*n)! * [x^(2*n)] cosh(x*tan(x/2)).
%e A296856 cosh(x*tan(x/2)) = 1 + 3*x^4/4! + 15*x^6/6! + 224*x^8/8! + 4545*x^10/10! + 126753*x^12/12! + ...
%t A296856 nmax = 17; Table[(CoefficientList[Series[Cosh[x Tan[x/2]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%Y A296856 Cf. A001469, A003711, A009166, A110501, A296839, A296841, A296842, A296853, A296854.
%K A296856 nonn
%O A296856 0,3
%A A296856 _Ilya Gutkovskiy_, Dec 21 2017