A326211 Number of unsortable normal multiset partitions of weight n.

0, 0, 0, 1, 17, 170, 1455, 11678, 92871, 752473

Offset: 0

Author

Gus Wiseman, Jun 19 2019

Keywords

• nonn
• more

Comments

A multiset partition is normal if it covers an initial interval of positive integers. It is unsortable if no permutation has an ordered concatenation, or equivalently if the concatenation of its lexicographically-ordered parts is not weakly increasing. For example, the multiset partition {{1,2},{1,1,1},{2,2,2}} is sortable because the permutation ((1,1,1),(1,2),(2,2,2)) has concatenation (1,1,1,1,2,2,2,2), which is weakly increasing.

Examples

			The a(3) = 1 and a(4) = 17 multiset partitions:
  {{1,3},{2}}  {{1,1,3},{2}}
               {{1,2},{1,2}}
               {{1,2},{1,3}}
               {{1,2,3},{2}}
               {{1,2,4},{3}}
               {{1,3},{2,2}}
               {{1,3},{2,3}}
               {{1,3},{2,4}}
               {{1,3,3},{2}}
               {{1,3,4},{2}}
               {{1,4},{2,3}}
               {{1},{1,3},{2}}
               {{1},{2,4},{3}}
               {{1,3},{2},{2}}
               {{1,3},{2},{3}}
               {{1,3},{2},{4}}
               {{1,4},{2},{3}}
		

Crossrefs

Unsortable set partitions are A058681.

Sortable normal multiset partitions are A326212.

Non-crossing normal multiset partitions are A324171.

MM-numbers of unsortable multiset partitions are A326258.

Cf. A000108, A016098, A255906, A324170.

Cf. A326209, A326210, A326243, A326250, A326255, A326256.

Programs

Mathematica

lexsort[f_,c_]:=OrderedQ[PadRight[{f,c}]];
allnorm[n_]:=If[n<=0,{{}},Function[s,Array[Count[s,y_/;y<=#]+1&,n]]/@Subsets[Range[n-1]+1]];
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]]]];
Table[Length[Select[Sort[#,lexsort]&/@Join@@mps/@allnorm[n],!OrderedQ[Join@@#]&]],{n,0,5}]

Formula

A255906(n) = a(n) + A326212(n).