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 A067309 #11 Dec 06 2020 17:18:04 %S A067309 0,0,2,9,82,1607,95647,18545153 %N A067309 Number of symmetric unlabeled digraphs (unlabeled digraphs with nontrivial automorphism group). %F A067309 a(n) = A000273(n) - A051504(n). %e A067309 For n=4 nodes from the 218 (=A000273(4)) unlabeled nonisomorphic digraphs 136 (=A051504(4)) are asymmetric, so 218 - 136 = 82 are somehow symmetric. %Y A067309 Cf. A000273, A051504. %K A067309 nonn,more %O A067309 0,3 %A A067309 _Labos Elemer_, Jan 11 2002 %E A067309 a(7) added using nauty by _Andrew Howroyd_, Dec 06 2020