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A330196
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Number of unlabeled set-systems covering n vertices with no endpoints.
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1
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OFFSET
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0,4
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COMMENTS
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A set-system is a finite set of finite nonempty sets. An endpoint is a vertex appearing only once (degree 1).
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LINKS
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EXAMPLE
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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}
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CROSSREFS
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First differences of the non-covering version A330124.
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.
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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