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A362050
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Numbers whose prime indices satisfy: (length) = 2*(median).
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5
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4, 54, 81, 90, 100, 126, 135, 140, 189, 198, 220, 234, 260, 297, 306, 340, 342, 351, 380, 414, 459, 460, 513, 522, 558, 580, 620, 621, 666, 738, 740, 774, 783, 820, 837, 846, 860, 940, 954, 999, 1060, 1062, 1098, 1107, 1161, 1180, 1206, 1220, 1269, 1278, 1314
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OFFSET
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1,1
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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).
All terms are squarefree.
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LINKS
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EXAMPLE
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The terms together with their prime indices begin:
4: {1,1}
54: {1,2,2,2}
81: {2,2,2,2}
90: {1,2,2,3}
100: {1,1,3,3}
126: {1,2,2,4}
135: {2,2,2,3}
140: {1,1,3,4}
189: {2,2,2,4}
198: {1,2,2,5}
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MATHEMATICA
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prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], PrimeOmega[#]==2*Median[prix[#]]&]
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CROSSREFS
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Before multiplying the median by 2, A361800 counts partitions of this type.
Partitions of this type are counted by A362049.
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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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