A330196 - OEIS

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A330196

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

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`

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