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 A305999 #11 Aug 14 2019 01:48:40
%S A305999 1,0,1,6,76,12916
%N A305999 Number of unlabeled spanning intersecting set-systems on n vertices with no singletons.
%C A305999 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. A singleton is an edge containing only one vertex.
%F A305999 a(n) = A306001(n) - A306001(n-1) for n > 0. - _Andrew Howroyd_, Aug 12 2019
%e A305999 Non-isomorphic representative of the a(3) = 6 set-systems:
%e A305999 {{1,2,3}}
%e A305999 {{1,3},{2,3}}
%e A305999 {{2,3},{1,2,3}}
%e A305999 {{1,2},{1,3},{2,3}}
%e A305999 {{1,3},{2,3},{1,2,3}}
%e A305999 {{1,2},{1,3},{2,3},{1,2,3}}
%Y A305999 Cf. A001206, A051185, A048143, A261006, A058891, A261005, A304998, A305854-A305857, A305935, A306000, A306001, A306008.
%K A305999 nonn,more
%O A305999 0,4
%A A305999 _Gus Wiseman_, Jun 16 2018
%E A305999 a(5) from _Andrew Howroyd_, Aug 12 2019