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 A305854 #13 Apr 28 2025 15:01:44
%S A305854 1,1,2,10,110,14868,1289830592
%N A305854 Number of unlabeled spanning intersecting set-systems on n vertices.
%C A305854 An intersecting set-system S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. S is spanning if every vertex is contained in some edge.
%F A305854 a(n) = A305856(n) - A305856(n-1) for n > 0. - _Andrew Howroyd_, Aug 12 2019
%e A305854 Non-isomorphic representatives of the a(3) = 10 spanning intersecting set-systems:
%e A305854 {{1,2,3}}
%e A305854 {{3},{1,2,3}}
%e A305854 {{1,3},{2,3}}
%e A305854 {{2,3},{1,2,3}}
%e A305854 {{3},{1,3},{2,3}}
%e A305854 {{3},{2,3},{1,2,3}}
%e A305854 {{1,2},{1,3},{2,3}}
%e A305854 {{1,3},{2,3},{1,2,3}}
%e A305854 {{3},{1,3},{2,3},{1,2,3}}
%e A305854 {{1,2},{1,3},{2,3},{1,2,3}}
%Y A305854 Cf. A001206, A006126, A051185, A261006, A283877, A304998, A305843, A305844, A305855-A305857.
%K A305854 nonn,more
%O A305854 0,3
%A A305854 _Gus Wiseman_, Jun 11 2018
%E A305854 a(5) from _Andrew Howroyd_, Aug 12 2019
%E A305854 a(6) from _Bert Dobbelaere_, Apr 28 2025