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A321469
Number of factorizations of n into factors > 1 with different sums of prime indices. Number of multiset partitions of the multiset of prime indices of n with distinct block-sums.
20
1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 2, 2, 1, 3, 1, 3, 2, 2, 1, 4, 1, 2, 2, 3, 1, 4, 1, 3, 2, 2, 2, 5, 1, 2, 2, 4, 1, 5, 1, 3, 3, 2, 1, 6, 1, 3, 2, 3, 1, 5, 2, 5, 2, 2, 1, 7, 1, 2, 2, 4, 2, 5, 1, 3, 2, 4, 1, 8, 1, 2, 3, 3, 2, 5, 1, 6, 2, 2, 1, 7, 2, 2, 2
OFFSET
1,6
COMMENTS
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798. The sum of prime indices of n is A056239(n).
EXAMPLE
The a(72) = 8 multiset partitions with distinct block-sums:
{{1,1,1,2,2}}
{{1},{1,1,2,2}}
{{2},{1,1,1,2}}
{{1,1},{1,2,2}}
{{1,2},{1,1,2}}
{{2,2},{1,1,1}}
{{1},{2},{1,1,2}}
{{1},{1,1},{2,2}}
Missing from this list are:
{{1},{1},{1,2,2}}
{{1},{1,2},{1,2}}
{{2},{2},{1,1,1}}
{{2},{1,1},{1,2}}
{{1},{1},{1},{2,2}}
{{1},{1},{2},{1,2}}
{{1},{2},{2},{1,1}}
{{1},{1},{1},{2},{2}}
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
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[mps[primeMS[n]], UnsameQ@@Sort[Total/@#]&]], {n, 100}]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 11 2018
STATUS
approved