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.
FORMULA
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
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