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A305855 Number of unlabeled spanning intersecting antichains on n vertices. 2
1, 1, 1, 3, 9, 72 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

An intersecting antichain S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection, and none of which is a subset of any other. S is spanning if every vertex is contained in some edge.

LINKS

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

EXAMPLE

Non-isomorphic representatives of the a(4) = 9 spanning intersecting antichains:

  {{1,2,3,4}}

  {{1,4},{2,3,4}}

  {{1,3,4},{2,3,4}}

  {{1,2},{1,3,4},{2,3,4}}

  {{1,3},{1,4},{2,3,4}}

  {{1,4},{2,4},{3,4}}

  {{1,2,4},{1,3,4},{2,3,4}}

  {{1,2},{1,3},{1,4},{2,3,4}}

  {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}

CROSSREFS

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

Sequence in context: A084543 A318030 A018564 * A004167 A321539 A163632

Adjacent sequences:  A305852 A305853 A305854 * A305856 A305857 A305858

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Jun 11 2018

STATUS

approved

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Last modified March 25 15:02 EDT 2019. Contains 321470 sequences. (Running on oeis4.)