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A317791 Number of non-isomorphic multiset partitions of the multiset of prime indices of n (row n of A112798). 22
1, 1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 4, 1, 2, 2, 5, 1, 4, 1, 4, 2, 2, 1, 7, 2, 2, 3, 4, 1, 3, 1, 7, 2, 2, 2, 7, 1, 2, 2, 7, 1, 3, 1, 4, 4, 2, 1, 12, 2, 4, 2, 4, 1, 7, 2, 7, 2, 2, 1, 9, 1, 2, 4, 11, 2, 3, 1, 4, 2, 3, 1, 16, 1, 2, 4, 4, 2, 3, 1, 12, 5, 2, 1, 9, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

A prime index of n is a number m such that prime(m) divides n.

a(n) depends only on prime signature of n (cf. A025487).  - Antti Karttunen, Dec 03 2018

LINKS

Gus Wiseman, Table of n, a(n) for n = 1..1000

Index entries for sequences computed from exponents in factorization of n

FORMULA

For all n, a(n) <= A001055(n). - Antti Karttunen, Dec 01 2018

If n is squarefree with k prime factors, or if n = p^k for p prime, we have a(n) = A000041(k).

EXAMPLE

Non-isomorphic representatives of the a(42) = 3 multiset partitions are {{1,2,4}}, {{1},{2,4}}, {{1},{2},{4}}.

Non-isomorphic representatives of the a(60) = 9 multiset partitions:

  {1123},

  {1}{123}, {2}{113}, {11}{23}, {12}{13},

  {1}{1}{23}, {1}{2}{13}, {2}{3}{11},

  {1}{1}{2}{3}.

Missing from this list are {3}{112} and {1}{3}{12}, which are isomorphic to {2}{113} and {1}{2}{13} respectively.

For n = 180 = 2^2 * 3^2 * 5, there are A001055(180) = 26 different factorizations to one or more factors larger than 1. Of these 18 are such that by swapping 2 and 3 in each factor of that factorization the result is another, different factorization of 180, while the other 8 cases are such that 2 <-> 3 swap doesn't change the factorization. Thus a(180) = 18/2 + 8 = 17. - Antti Karttunen, Dec 03 2018

MATHEMATICA

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]]]];

sysnorm[{}] := {}; sysnorm[m_]:=If[Union@@m!=Range[Max@@Flatten[m]], sysnorm[m/.Rule@@@Table[{(Union@@m)[[i]], i}, {i, Length[Union@@m]}]], First[Sort[sysnorm[m, 1]]]]; sysnorm[m_, aft_]:=If[Length[Union@@m]<=aft, {m}, With[{mx=Table[Count[m, i, {2}], {i, Select[Union@@m, #>=aft&]}]}, Union@@(sysnorm[#, aft+1]&/@Union[Table[Map[Sort, m/.{par+aft-1->aft, aft->par+aft-1}, {0, 1}], {par, First/@Position[mx, Max[mx]]}]])]];

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

Table[Length[Union[sysnorm/@mps[primeMS[n]]]], {n, 100}]

CROSSREFS

Cf. A001055, A007716, A045778, A056239, A112798, A281116, A317533, A317757.

Sequence in context: A317508 A323438 A317141 * A318559 A218320 A305254

Adjacent sequences:  A317788 A317789 A317790 * A317792 A317793 A317794

KEYWORD

nonn

AUTHOR

Gus Wiseman, Aug 07 2018

EXTENSIONS

Terms corrected by Gus Wiseman, Dec 04 2018

STATUS

approved

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Last modified April 26 04:11 EDT 2019. Contains 322469 sequences. (Running on oeis4.)