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A360006
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Least positive integer whose prime indices have median n/2. a(1) = 1.
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27
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1, 2, 6, 3, 14, 5, 26, 7, 38, 11, 58, 13, 74, 17, 86, 19, 106, 23, 122, 29, 142, 31, 158, 37, 178, 41, 202, 43, 214, 47, 226, 53, 262, 59, 278, 61, 302, 67, 326, 71, 346, 73, 362, 79, 386, 83, 398, 89, 446, 97, 458, 101, 478, 103, 502, 107, 526, 109, 542, 113
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OFFSET
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1,2
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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.
The median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length).
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LINKS
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FORMULA
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MATHEMATICA
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nn=100;
prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
seq=Table[If[n==1, 1, 2*Median[prix[n]]], {n, nn}];
Table[Position[seq, k][[1, 1]], {k, Count[Differences[Union[seq]], 1]}]
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CROSSREFS
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Position of first appearance of n in A360005.
A316413 lists numbers whose prime indices have integer mean.
A359908 = numbers w/ integer median of prime indices, complement A359912.
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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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