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A305856 Number of unlabeled intersecting set-systems on up to n vertices. 3
1, 2, 4, 14, 124, 14992 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

An intersecting set-system is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection.

LINKS

Table of n, a(n) for n=0..5.

EXAMPLE

Non-isomorphic representatives of the a(3) = 14 intersecting set-systems:

  {}

  {{1}}

  {{1,2}}

  {{1,2,3}}

  {{2},{1,2}}

  {{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}}

CROSSREFS

Cf. A001206, A006126, A051185, A261006, A283877, A304982, A304996, A304998, A305843, A305844, A305854-A305857.

Sequence in context: A102449 A193520 A102897 * A001527 A067209 A134040

Adjacent sequences:  A305853 A305854 A305855 * A305857 A305858 A305859

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Jun 11 2018

EXTENSIONS

a(5) from Andrew Howroyd, Aug 12 2019

STATUS

approved

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Last modified December 6 07:00 EST 2019. Contains 329784 sequences. (Running on oeis4.)