OFFSET
0,3
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.
EXAMPLE
Non-isomorphic representatives of the a(0) = 1 through a(4) = 10 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}}
{{1},{2,4},{3,4}}
{{1},{2,3},{2,4},{3,4}}
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 26 2019
STATUS
approved