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A327808
Number of unlabeled, disconnected, nonempty antichains of subsets of {1..n}.
2
0, 0, 1, 3, 9, 32, 233, 16578
OFFSET
0,4
COMMENTS
An antichain is a set of nonempty sets, none of which is a subset of any other. A singleton is considered to be connected.
FORMULA
a(n) = A327424(n) - 1.
EXAMPLE
Non-isomorphic representatives of the a(2) = 1 through a(4) = 9 antichains:
{{1},{2}} {{1},{2}} {{1},{2}}
{{1},{2,3}} {{1},{2,3}}
{{1},{2},{3}} {{1},{2},{3}}
{{1},{2,3,4}}
{{1,2},{3,4}}
{{1},{2},{3,4}}
{{1},{2},{3},{4}}
{{2},{1,3},{1,4}}
{{4},{1,2},{1,3},{2,3}}
CROSSREFS
The labeled version is A327354 - 1.
The covering case is A327426.
Unlabeled antichains that are either not connected or not covering are A327437.
The version with empty antichains allowed is A327424.
Sequence in context: A341302 A297209 A058138 * A284964 A344247 A333770
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 26 2019
STATUS
approved