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 A326223 #7 Jun 16 2019 22:34:28
%S A326223 1,0,7,80,2186
%N A326223 Number of non-Hamiltonian unlabeled n-vertex digraphs (with loops).
%C A326223 A digraph is Hamiltonian if it contains a directed cycle passing through every vertex exactly once.
%H A326223 Gus Wiseman, <a href="/A326223/a326223_1.png">Non-isomorphic representatives of the a(3) = 80 non-Hamiltonian digraphs</a>.
%e A326223 Non-isomorphic representatives of the a(2) = 7 digraph edge-sets:
%e A326223 {}
%e A326223 {11}
%e A326223 {12}
%e A326223 {11,12}
%e A326223 {11,21}
%e A326223 {11,22}
%e A326223 {11,12,22}
%Y A326223 The labeled case is A326220.
%Y A326223 The case without loops is A326222.
%Y A326223 The undirected case is A246446 (without loops) or A326239 (with loops).
%Y A326223 Hamiltonian unlabeled digraphs are A326226.
%Y A326223 Unlabeled digraphs not containing a Hamiltonian path are A326224.
%Y A326223 Cf. A000595, A002416, A003087, A003216, A283420, A326204, A326218, A326225.
%K A326223 nonn,more
%O A326223 0,3
%A A326223 _Gus Wiseman_, Jun 15 2019