|
%I #19 May 11 2020 09:50:17
%S 1,2,3,6,15,87,3528,47174113
%N Number of unlabeled intersecting antichains on up to n vertices.
%C 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.
%F a(n) = A305855(0) + A305855(1) + ... + A305855(n). - _Brendan McKay_, May 11 2020
%e Non-isomorphic representatives of the a(4) = 15 intersecting antichains:
%e {}
%e {{1}}
%e {{1,2}}
%e {{1,2,3}}
%e {{1,2,3,4}}
%e {{1,3},{2,3}}
%e {{1,4},{2,3,4}}
%e {{1,3,4},{2,3,4}}
%e {{1,2},{1,3},{2,3}}
%e {{1,4},{2,4},{3,4}}
%e {{1,3},{1,4},{2,3,4}}
%e {{1,2},{1,3,4},{2,3,4}}
%e {{1,2,4},{1,3,4},{2,3,4}}
%e {{1,2},{1,3},{1,4},{2,3,4}}
%e {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}
%Y Cf. A001206, A006126, A051185, A261006, A283877, A304998, A305843, A305844, A305854, A305855, A305856.
%K nonn,more
%O 0,2
%A _Gus Wiseman_, Jun 11 2018
%E a(6) from _Andrew Howroyd_, Aug 13 2019
%E a(7) from _Brendan McKay_, May 11 2020
|
