A330124 - OEIS

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

A330124

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

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`

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