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A305854
Number of unlabeled spanning intersecting set-systems on n vertices.
41
1, 1, 2, 10, 110, 14868
OFFSET
0,3
COMMENTS
An intersecting set-system S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. S is spanning if every vertex is contained in some edge.
FORMULA
a(n) = A305856(n) - A305856(n-1) for n > 0. - Andrew Howroyd, Aug 12 2019
EXAMPLE
Non-isomorphic representatives of the a(3) = 10 spanning intersecting set-systems:
{{1,2,3}}
{{3},{1,2,3}}
{{1,3},{2,3}}
{{2,3},{1,2,3}}
{{3},{1,3},{2,3}}
{{3},{2,3},{1,2,3}}
{{1,2},{1,3},{2,3}}
{{1,3},{2,3},{1,2,3}}
{{3},{1,3},{2,3},{1,2,3}}
{{1,2},{1,3},{2,3},{1,2,3}}
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Jun 11 2018
EXTENSIONS
a(5) from Andrew Howroyd, Aug 12 2019
STATUS
approved