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A367095
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Number of distinct sums of pairs (repeats allowed) of prime indices of n.
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9
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0, 1, 1, 1, 1, 3, 1, 1, 1, 3, 1, 3, 1, 3, 3, 1, 1, 3, 1, 3, 3, 3, 1, 3, 1, 3, 1, 3, 1, 5, 1, 1, 3, 3, 3, 3, 1, 3, 3, 3, 1, 6, 1, 3, 3, 3, 1, 3, 1, 3, 3, 3, 1, 3, 3, 3, 3, 3, 1, 5, 1, 3, 3, 1, 3, 6, 1, 3, 3, 6, 1, 3, 1, 3, 3, 3, 3, 6, 1, 3, 1, 3, 1, 6, 3, 3, 3
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OFFSET
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1,6
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COMMENTS
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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.
Is the image missing only 2 and 4?
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LINKS
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EXAMPLE
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The prime indices of 15 are {2,3}, with sums of pairs:
2+2 = 4
2+3 = 5
3+3 = 6
so a(15) = 3.
The prime indices of 180 are {1,1,2,2,3}, with sums of pairs:
1+1 = 2
1+2 = 3
1+3 = 4
2+2 = 4
2+3 = 5
3+3 = 6
so a(180) = 5.
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MATHEMATICA
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prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Table[Length[Union[Total/@Tuples[prix[n], 2]]], {n, 100}]
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CROSSREFS
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Depends only on squarefree kernel A007947.
Positions of first appearances appear to be a subset of A325986.
For 2-element submultisets we have A366739, for all submultisets A299701.
A304793 counts positive subset-sums of prime indices.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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