login
A330196
Number of unlabeled set-systems covering n vertices with no endpoints.
1
1, 0, 1, 20, 1754
OFFSET
0,4
COMMENTS
A set-system is a finite set of finite nonempty sets. An endpoint is a vertex appearing only once (degree 1).
EXAMPLE
Non-isomorphic representatives of the a(3) = 20 set-systems:
{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 non-covering version A330124.
The "multi" version is A302545.
Unlabeled set-systems with no endpoints counted by vertices are A317794.
Unlabeled set-systems with no endpoints counted by weight are A330054.
Unlabeled set-systems counted by vertices are A000612.
Unlabeled set-systems counted by weight are A283877.
Sequence in context: A177296 A177297 A014606 * A172556 A246619 A222973
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Dec 05 2019
STATUS
approved