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Number of unlabeled clutters (connected antichains) spanning up to n vertices without singleton edges.
7

%I #8 May 23 2018 23:12:46

%S 1,1,2,5,19,176,16118,489996568

%N Number of unlabeled clutters (connected antichains) spanning up to n vertices without singleton edges.

%F Partial sums of A261006(n > 0).

%e Non-isomorphic representatives of the a(3) = 5 clutters:

%e {}

%e {{1,2}}

%e {{1,2,3}}

%e {{1,3},{2,3}}

%e {{1,2},{1,3},{2,3}}

%e Non-isomorphic representatives of the a(4) = 19 clutters:

%e {}

%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 {{1,2},{1,3,4},{2,3,4}}

%e {{1,3},{1,4},{2,3,4}}

%e {{1,3},{2,4},{3,4}}

%e {{1,4},{2,4},{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},{1,3},{2,4},{3,4}}

%e {{1,4},{2,3},{2,4},{3,4}}

%e {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}

%e {{1,3},{1,4},{2,3},{2,4},{3,4}}

%e {{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}

%Y Cf. A048143, A198085, A261006, A304912, A304981, A304982, A304983, A304984, A304985, A304986.

%K nonn

%O 0,3

%A _Gus Wiseman_, May 23 2018