

A330196


Number of unlabeled setsystems covering n vertices with no endpoints.


1




OFFSET

0,4


COMMENTS

A setsystem is a finite set of finite nonempty sets. An endpoint is a vertex appearing only once (degree 1).


LINKS



EXAMPLE

Nonisomorphic representatives of the a(3) = 20 setsystems:
{12}{13}{23}
{1}{23}{123}
{12}{13}{123}
{1}{2}{13}{23}
{1}{2}{3}{123}
{1}{12}{13}{23}
{1}{2}{13}{123}
{1}{12}{13}{123}
{1}{12}{23}{123}
{12}{13}{23}{123}
{1}{2}{3}{12}{13}
{1}{2}{12}{13}{23}
{1}{2}{3}{12}{123}
{1}{2}{12}{13}{123}
{1}{2}{13}{23}{123}
{1}{12}{13}{23}{123}
{1}{2}{3}{12}{13}{23}
{1}{2}{3}{12}{13}{123}
{1}{2}{12}{13}{23}{123}
{1}{2}{3}{12}{13}{23}{123}


CROSSREFS

First differences of the noncovering version A330124.
Unlabeled setsystems with no endpoints counted by vertices are A317794.
Unlabeled setsystems with no endpoints counted by weight are A330054.
Unlabeled setsystems counted by vertices are A000612.
Unlabeled setsystems counted by weight are A283877.


KEYWORD

nonn,more


AUTHOR



STATUS

approved



