cp's OEIS Frontend

A330124 Number of unlabeled set-systems with n vertices and no endpoints.

%I A330124 #7 Dec 06 2019 09:36:30
%S A330124 1,1,2,22,1776
%N A330124 Number of unlabeled set-systems with n vertices and no endpoints.
%C A330124 A set-system is a finite set of finite nonempty sets. An endpoint is a vertex appearing only once (degree 1).
%e A330124 Non-isomorphic representatives of the a(3) = 22 set-systems:
%e A330124   0
%e A330124   {1}{2}{12}
%e A330124   {12}{13}{23}
%e A330124   {1}{23}{123}
%e A330124   {12}{13}{123}
%e A330124   {1}{2}{13}{23}
%e A330124   {1}{2}{3}{123}
%e A330124   {1}{12}{13}{23}
%e A330124   {1}{2}{13}{123}
%e A330124   {1}{12}{13}{123}
%e A330124   {1}{12}{23}{123}
%e A330124   {12}{13}{23}{123}
%e A330124   {1}{2}{3}{12}{13}
%e A330124   {1}{2}{12}{13}{23}
%e A330124   {1}{2}{3}{12}{123}
%e A330124   {1}{2}{12}{13}{123}
%e A330124   {1}{2}{13}{23}{123}
%e A330124   {1}{12}{13}{23}{123}
%e A330124   {1}{2}{3}{12}{13}{23}
%e A330124   {1}{2}{3}{12}{13}{123}
%e A330124   {1}{2}{12}{13}{23}{123}
%e A330124   {1}{2}{3}{12}{13}{23}{123}
%Y A330124 Partial sums of the covering case A330196.
%Y A330124 The labeled version is A330059.
%Y A330124 The "multi" version is A302545.
%Y A330124 Unlabeled set-systems with no endpoints counted by weight are A330054.
%Y A330124 Unlabeled set-systems with no singletons are A317794.
%Y A330124 Unlabeled set-systems counted by vertices are A000612.
%Y A330124 Unlabeled set-systems counted by weight are A283877.
%Y A330124 The case with no singletons is A320665.
%Y A330124 Cf. A007716, A016031, A306005, A317795, A321405, A330052, A330055.
%K A330124 nonn,more
%O A330124 0,3
%A A330124 _Gus Wiseman_, Dec 05 2019