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A330196 Number of unlabeled set-systems covering n vertices with no endpoints. 1
1, 0, 1, 20, 1754 (list; graph; refs; listen; history; text; internal format)
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).

LINKS

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

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.

Cf. A007716, A016031, A306005, A317795, A320665, A330052, A330053, A330055.

Sequence in context: A177296 A177297 A014606 * A172556 A246619 A222973

Adjacent sequences:  A330193 A330194 A330195 * A330197 A330198 A330199

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Dec 05 2019

STATUS

approved

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Last modified August 8 14:04 EDT 2020. Contains 336298 sequences. (Running on oeis4.)