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A319646
Number of non-isomorphic weight-n chains of distinct multisets whose dual is also a chain of distinct multisets.
37
1, 1, 1, 4, 4, 9, 17, 28, 41, 75, 122, 192, 314, 484, 771, 1216, 1861, 2848, 4395, 6610, 10037
OFFSET
0,4
COMMENTS
The dual of a multiset partition has, for each vertex, one block consisting of the indices (or positions) of the blocks containing that vertex, counted with multiplicity. For example, the dual of {{1,2},{2,2}} is {{1},{1,2,2}}.
The weight of a multiset partition is the sum of sizes of its parts. Weight is generally not the same as number of vertices.
From Gus Wiseman, Jan 17 2019: (Start)
Also the number of plane partitions of n with no repeated rows or columns. For example, the a(6) = 17 plane partitions are:
6 51 42 321
.
5 4 41 31 32 31 22 221 211
1 2 1 2 1 11 2 1 11
.
3 21 21 111
2 2 11 11
1 1 1 1
(End)
EXAMPLE
Non-isomorphic representatives of the a(1) = 1 through a(5) = 9 chains:
1: {{1}}
2: {{1,1}}
3: {{1,1,1}}
{{1,2,2}}
{{1},{1,1}}
{{2},{1,2}}
4: {{1,1,1,1}}
{{1,2,2,2}}
{{1},{1,1,1}}
{{2},{1,2,2}}
5: {{1,1,1,1,1}}
{{1,1,2,2,2}}
{{1,2,2,2,2}}
{{1},{1,1,1,1}}
{{2},{1,1,2,2}}
{{2},{1,2,2,2}}
{{1,1},{1,1,1}}
{{1,2},{1,2,2}}
{{2,2},{1,2,2}}
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
ptnplane[n_]:=Union[Map[Reverse@*primeMS, Join@@Permutations/@facs[n], {2}]];
Table[Sum[Length[Select[ptnplane[Times@@Prime/@y], And[UnsameQ@@#, UnsameQ@@Transpose[PadRight[#]], And@@GreaterEqual@@@#, And@@(GreaterEqual@@@Transpose[PadRight[#]])]&]], {y, IntegerPartitions[n]}], {n, 10}] (* Gus Wiseman, Jan 18 2019 *)
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 25 2018
EXTENSIONS
a(11)-a(17) from Gus Wiseman, Jan 18 2019
a(18)-a(21) from Robert Price, Jun 21 2021
STATUS
approved