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 A296791 #4 Dec 20 2017 23:36:58
%S A296791 1,-1,-7,-1,3121,132959,-1261591,-889217057,-79029091743,
%T A296791 5889540654911,3289057601679065,395957721046153023,
%U A296791 -120519140613246313327,-71865162873642033099361,-9267049529998625177827639,8376363338336819515365004319,5693280488360087435524724806849
%N A296791 Expansion of e.g.f. sech(x*sec(x)) (even powers only).
%F A296791 a(n) = (2*n)! * [x^(2*n)] sech(x*sec(x)).
%e A296791 sech(x*sec(x)) = 1 - x^2/2! - 7*x^4/4! - x^6/6! + 3121*x^8/8! + ...
%t A296791 nmax = 16; Table[(CoefficientList[Series[Sech[x Sec[x]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%Y A296791 Cf. A000364, A003721, A003722, A009008, A009009, A009010, A009011, A009015, A009016, A009118, A009562, A009765, A102072, A102075, A296731, A296740, A296790.
%K A296791 sign
%O A296791 0,3
%A A296791 _Ilya Gutkovskiy_, Dec 20 2017