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A349739 Number of ordered pairs of commuting elements (partial permutations) in the symmetric inverse semigroup on [n]. 1
1, 4, 31, 310, 3925, 58936, 1032979, 20600266, 461742985 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
REFERENCES
Stephen Lipscomb, Symmetric Inverse Semigroups, Mathematical Surveys and Monographs, Volume 46, 1996, Chapters 3,4,5.
LINKS
MATHEMATICA
x[list_] := If[list == {}, 1, Apply[Times, list] Apply[Times, Table[Count[list, i]!, {i, 1, Max[list]}]]]; y[list_] := If[list == {}, 1, Apply[Times, Table[Count[list, i]!, {i, 1, Max[list]}]]];
c[n_, pair_] := n!/(x[pair[[1]]] y[pair[[2]]]); n[k_, list_] := Count[list, k];
m[k_, list_] := Sum[Binomial[n[k, list], j]^2 j! k^j, {j, 0, n[k, list]}];
xp[list_] := Apply[Times, Table[m[k, list], {k, 1, Max[{1, list}]}]];
partialPermMatrices1[n_] := Module[{im = PadRight[IdentityMatrix[n], {n + 1, n}]},
Sort@Map[Extract[im, List /@ #] &]@ Permutations[Join[ConstantArray[n + 1, n], Range@n], {n}]]; s[list_] := Total[Map[Apply[Times, #] &, Map[Min, Map[list[[#]] &, Map[Position[#, 1] &, partialPermMatrices1[Length[list]]], {2}], {2}]]]; Table[(Map[s, Level[Table[Level[Table[Table[{IntegerPartitions[nn - k][[i]], IntegerPartitions[k][[j]]}, {i, 1, PartitionsP[nn - k]}], {j, 1, PartitionsP[k]}], {2}], {k, 0, nn}], {2}][[All, 2]]])*(Map[xp, Level[Table[ Level[Table[Table[{IntegerPartitions[nn - k][[i]], IntegerPartitions[k][[j]]}, {i, 1, PartitionsP[nn - k]}], {j, 1, PartitionsP[k]}], {2}], {k, 0, nn}], {2}][[All, 1]]])*(Map[c[nn, #] &, Level[Table[Level[Table[Table[{IntegerPartitions[nn - k][[i]], IntegerPartitions[k][[j]]}, {i, 1, PartitionsP[nn - k]}], {j, 1, PartitionsP[k]}], {2}], {k, 0, nn}], {2}]]) // Total, {nn, 0, 7}]
CROSSREFS
Cf. A002720, A000712 (number of conjugacy classes).
Sequence in context: A199683 A114475 A243312 * A359621 A076280 A141005
KEYWORD
nonn,more
AUTHOR
Geoffrey Critzer, Dec 19 2021
STATUS
approved

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Last modified April 23 19:56 EDT 2024. Contains 371916 sequences. (Running on oeis4.)