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A306001
Number of unlabeled intersecting set-systems with no singletons on up to n vertices.
3
1, 1, 2, 8, 84, 13000
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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. A singleton is an edge containing only one vertex.
LINKS
Table of n, a(n) for n=0..5.
FORMULA
a(n) =
A305856
(n) -
A000612
(n). -
Andrew Howroyd
, Aug 12 2019
EXAMPLE
Non-isomorphic representatives of the a(3) = 8 set-systems:
{}
{{1,2}}
{{1,2,3}}
{{1,3},{2,3}}
{{2,3},{1,2,3}}
{{1,2},{1,3},{2,3}}
{{1,3},{2,3},{1,2,3}}
{{1,2},{1,3},{2,3},{1,2,3}}
CROSSREFS
Cf.
A001206
,
A051185
,
A048143
,
A261006
,
A058891
,
A261005
,
A304998
,
A305854
-
A305857
,
A305935
,
A305999
,
A306000
.
Sequence in context:
A261683
A134089
A136647
*
A261730
A052456
A276991
Adjacent sequences:
A305998
A305999
A306000
*
A306002
A306003
A306004
KEYWORD
nonn
,
more
AUTHOR
Gus Wiseman
, Jun 16 2018
EXTENSIONS
a(5) from
Andrew Howroyd
, Aug 12 2019
STATUS
approved
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Last modified September 4 09:09 EDT 2024. Contains 375681 sequences. (Running on oeis4.)