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 A330528 #4 Dec 17 2019 19:14:05
%S A330528 1,17,421,29945,1864921,382577645,43788506581,15558403000145,
%T A330528 3746015060385841,1757547389533786325,562069712763196977901,
%U A330528 516878970296221633758905,201649817635812110915892361,216661054181289983631892988285
%N A330528 Expansion of e.g.f. Sum_{k>=1} (sec(x^k) - 1) (even powers only).
%F A330528 a(n) = (2*n)! * Sum_{d|n} A000364(d) / (2*d)!.
%t A330528 nmax = 14; Table[(CoefficientList[Series[Sum[(Sec[x^k] - 1), {k, 1, nmax}], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}] // Rest
%t A330528 Table[(2 n)! DivisorSum[n, Abs[EulerE[2 #]]/(2 #)! &], {n, 1, 14}]
%Y A330528 Cf. A000364, A028296, A176474, A330255, A330527.
%K A330528 nonn
%O A330528 1,2
%A A330528 _Ilya Gutkovskiy_, Dec 17 2019