login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A330124 Number of unlabeled set-systems with n vertices and no endpoints. 2
1, 1, 2, 22, 1776 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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

LINKS

Table of n, a(n) for n=0..4.

EXAMPLE

Non-isomorphic representatives of the a(3) = 22 set-systems:

  0

  {1}{2}{12}

  {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

Partial sums of the covering case A330196.

The labeled version is A330059.

The "multi" version is A302545.

Unlabeled set-systems with no endpoints counted by weight are A330054.

Unlabeled set-systems with no singletons are A317794.

Unlabeled set-systems counted by vertices are A000612.

Unlabeled set-systems counted by weight are A283877.

The case with no singletons is A320665.

Cf. A007716, A016031, A306005, A317795, A321405, A330052, A330055.

Sequence in context: A193486 A337577 A054948 * A104149 A113761 A319620

Adjacent sequences:  A330121 A330122 A330123 * A330125 A330126 A330127

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Dec 05 2019

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 5 00:01 EST 2021. Contains 341812 sequences. (Running on oeis4.)