OFFSET
0,3
COMMENTS
All sets and multisets must be finite, and only the outermost may be empty.
The weight of an atom is 1, and the weight of a multiset is the sum of weights of its elements, counting multiplicity.
EXAMPLE
Non-isomorphic representatives of the a(1) = 1 through a(3) = 13 sets of multisets of sets:
{{1}} {{12}} {{123}}
{{1}{1}} {{1}{12}}
{{1}{2}} {{1}{23}}
{{1}}{{2}} {{1}{1}{1}}
{{1}}{{12}}
{{1}{1}{2}}
{{1}}{{23}}
{{1}{2}{3}}
{{1}}{{1}{1}}
{{1}}{{1}{2}}
{{1}}{{2}{3}}
{{2}}{{1}{1}}
{{1}}{{2}}{{3}}
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Jan 27 2019
STATUS
approved