login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A305857 Number of unlabeled intersecting antichains on up to n vertices. 16
1, 2, 3, 6, 15, 87, 3528, 47174113 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

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.

LINKS

Table of n, a(n) for n=0..7.

FORMULA

a(n) = A305855(0) + A305855(1) + ... + A305855(n). - Brendan McKay, May 11 2020

EXAMPLE

Non-isomorphic representatives of the a(4) = 15 intersecting antichains:

  {}

  {{1}}

  {{1,2}}

  {{1,2,3}}

  {{1,2,3,4}}

  {{1,3},{2,3}}

  {{1,4},{2,3,4}}

  {{1,3,4},{2,3,4}}

  {{1,2},{1,3},{2,3}}

  {{1,4},{2,4},{3,4}}

  {{1,3},{1,4},{2,3,4}}

  {{1,2},{1,3,4},{2,3,4}}

  {{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, A305855, A305856.

Sequence in context: A116632 A214343 A007364 * A014627 A145781 A109162

Adjacent sequences:  A305854 A305855 A305856 * A305858 A305859 A305860

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Jun 11 2018

EXTENSIONS

a(6) from Andrew Howroyd, Aug 13 2019

a(7) from Brendan McKay, May 11 2020

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 1 16:44 EST 2021. Contains 349430 sequences. (Running on oeis4.)