OFFSET
0,3
COMMENTS
An interval such as {3,4,5} is a set of positive integers with all differences of adjacent elements equal to 1.
LINKS
EXAMPLE
The a(1) = 1 through a(4) = 18 multiset partitions:
{{1}} {{1,2}} {{1,2,3}} {{1,2,3,4}}
{{1},{1}} {{1},{1,2}} {{1},{1,2,3}}
{{1},{2}} {{1},{2,3}} {{1,2},{1,2}}
{{3},{1,2}} {{1},{2,3,4}}
{{1},{1},{1}} {{1,2},{3,4}}
{{1},{1},{2}} {{4},{1,2,3}}
{{1},{2},{3}} {{1},{1},{1,2}}
{{1},{1},{2,3}}
{{1},{2},{1,2}}
{{1},{2},{3,4}}
{{1},{3},{1,2}}
{{1},{4},{2,3}}
{{3},{4},{1,2}}
{{1},{1},{1},{1}}
{{1},{1},{1},{2}}
{{1},{1},{2},{2}}
{{1},{1},{2},{3}}
{{1},{2},{3},{4}}
MATHEMATICA
strnorm[n_]:=Flatten[MapIndexed[Table[#2, {#1}]&, #]]&/@IntegerPartitions[n];
sps[{}]:={{}}; sps[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@sps[Complement[set, s]]]/@Cases[Subsets[set], {i, ___}];
mps[set_]:=Union[Sort[Sort/@(#/.x_Integer:>set[[x]])]&/@sps[Range[Length[set]]]];
chQ[y_]:=Or[Length[y]<=1, Union[Differences[y]]=={1}];
Table[Length[Select[Join@@mps/@strnorm[n], And@@chQ/@#&]], {n, 0, 5}]
CROSSREFS
A011782 counts multisets covering an initial interval.
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 09 2022
STATUS
approved