

A275307


Number of labeled spanning blobs on n vertices.


38




OFFSET

1,3


COMMENTS

A clutter is a set of sets comprising a connected antichain in the Boolean algebra B_n. A blob is defined as a clutter that cannot be capped by a tree.


LINKS

Table of n, a(n) for n=1..8.
Louis J. Billera, On the Composition and Decomposition of Clutters, J. Combinatorial Theory 11, 234245 (1971).
Gus Wiseman, Every Clutter is a Tree of Blobs (preprint)


FORMULA

Every clutter is a tree of blobs, so we have A048143(n) = Sum_p n^(k1) Prod_i a(p_i+1), where the sum is over all set partitions U(p_1,...,p_k) = {1,...,n1}.


EXAMPLE

The a(3)=2 blobs are: {{1,2,3}}, {{1,2},{1,3},{2,3}}.


CROSSREFS

Cf. A048143 (clutters), A030019 (hypertrees), A052888 (tail trees).
Sequence in context: A290879 A054914 A329021 * A291808 A161745 A048566
Adjacent sequences: A275304 A275305 A275306 * A275308 A275309 A275310


KEYWORD

nonn,more


AUTHOR

Gus Wiseman, Jul 22 2016


STATUS

approved



