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 A326883 #9 Aug 11 2019 12:23:55
%S A326883 1,1,4,22,302,28630,216533404,5592325966377736
%N A326883 Number of unlabeled set-systems with {} that are closed under intersection and cover n vertices.
%F A326883 a(n) = A108800(n) - A108800(n-1) for n > 0. - _Andrew Howroyd_, Aug 10 2019
%e A326883 Non-isomorphic representatives of the a(0) = 1 through a(3) = 22 set-systems:
%e A326883 {{}} {{}{1}} {{}{12}} {{}{123}}
%e A326883 {{}{1}{2}} {{}{1}{23}}
%e A326883 {{}{2}{12}} {{}{3}{123}}
%e A326883 {{}{1}{2}{12}} {{}{1}{2}{3}}
%e A326883 {{}{23}{123}}
%e A326883 {{}{1}{3}{23}}
%e A326883 {{}{2}{3}{123}}
%e A326883 {{}{3}{13}{23}}
%e A326883 {{}{1}{23}{123}}
%e A326883 {{}{3}{23}{123}}
%e A326883 {{}{1}{2}{3}{23}}
%e A326883 {{}{1}{2}{3}{123}}
%e A326883 {{}{2}{3}{13}{23}}
%e A326883 {{}{1}{3}{23}{123}}
%e A326883 {{}{2}{3}{23}{123}}
%e A326883 {{}{3}{13}{23}{123}}
%e A326883 {{}{1}{2}{3}{13}{23}}
%e A326883 {{}{1}{2}{3}{23}{123}}
%e A326883 {{}{2}{3}{13}{23}{123}}
%e A326883 {{}{1}{2}{3}{12}{13}{23}}
%e A326883 {{}{1}{2}{3}{13}{23}{123}}
%e A326883 {{}{1}{2}{3}{12}{13}{23}{123}}
%Y A326883 The case also closed under union is A001930.
%Y A326883 The connected case (i.e., with maximum) is A108798.
%Y A326883 The same for union instead of intersection is (also) A108798.
%Y A326883 The non-covering case is A108800.
%Y A326883 The labeled case is A326881.
%Y A326883 Cf. A000798, A102894, A102895, A102897, A193674, A193675, A306445, A326875, A326878, A326880.
%K A326883 nonn,more
%O A326883 0,3
%A A326883 _Gus Wiseman_, Jul 30 2019
%E A326883 a(5)-a(7) from _Andrew Howroyd_, Aug 10 2019