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 A351883 #8 Feb 24 2022 02:16:33
%S A351883 1,1,2,3,6,35,285,2044,13804,108093,1083405,12281896,143452386,
%T A351883 1763156031,23845410407,353626471808,5579871336488,92609430408361,
%U A351883 1627509065584185,30379312334903408,598533509334403470,12366674489588950555,267527916985316556019
%N A351883 Expansion of e.g.f. 1 / (1 - x)^sech(x).
%F A351883 a(0) = 1; a(n) = -Sum_{k=1..n} (-1)^k * binomial(n-1,k-1) * A009435(k) * a(n-k).
%F A351883 a(n) ~ n! / (Gamma(1/cosh(1)) * n^(1 - 1/cosh(1))). - _Vaclav Kotesovec_, Feb 24 2022
%t A351883 nmax = 22; CoefficientList[Series[1/(1 - x)^Sech[x], {x, 0, nmax}], x] Range[0, nmax]!
%o A351883 (PARI) my(x='x+O('x^30)); Vec(serlaplace(1/(1-x)^(1/cosh(x)))) \\ _Michel Marcus_, Feb 23 2022
%Y A351883 Cf. A009197, A009435, A351881, A351882.
%K A351883 nonn
%O A351883 0,3
%A A351883 _Ilya Gutkovskiy_, Feb 23 2022