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A338318
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Composite numbers whose prime indices are pairwise intersecting (non-coprime).
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1
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9, 21, 25, 27, 39, 49, 57, 63, 65, 81, 87, 91, 111, 115, 117, 121, 125, 129, 133, 147, 159, 169, 171, 183, 185, 189, 203, 213, 235, 237, 243, 247, 259, 261, 267, 273, 289, 299, 301, 303, 305, 319, 321, 325, 333, 339, 343, 351, 361, 365, 371, 377, 387, 393
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OFFSET
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1,1
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COMMENTS
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First differs from A322336 in lacking 2535, with prime indices {2,3,6,6}.
First differs from A327685 in having 17719, with prime indices {6,10,15}.
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.
Also Heinz numbers of pairwise intersecting (non-coprime) partitions with more than one part. The Heinz number of a partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k), giving a bijective correspondence between positive integers and integer partitions.
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LINKS
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FORMULA
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EXAMPLE
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The sequence of terms together with their prime indices begins:
9: {2,2} 121: {5,5} 243: {2,2,2,2,2}
21: {2,4} 125: {3,3,3} 247: {6,8}
25: {3,3} 129: {2,14} 259: {4,12}
27: {2,2,2} 133: {4,8} 261: {2,2,10}
39: {2,6} 147: {2,4,4} 267: {2,24}
49: {4,4} 159: {2,16} 273: {2,4,6}
57: {2,8} 169: {6,6} 289: {7,7}
63: {2,2,4} 171: {2,2,8} 299: {6,9}
65: {3,6} 183: {2,18} 301: {4,14}
81: {2,2,2,2} 185: {3,12} 303: {2,26}
87: {2,10} 189: {2,2,2,4} 305: {3,18}
91: {4,6} 203: {4,10} 319: {5,10}
111: {2,12} 213: {2,20} 321: {2,28}
115: {3,9} 235: {3,15} 325: {3,3,6}
117: {2,2,6} 237: {2,22} 333: {2,2,12}
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MATHEMATICA
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stabstrQ[u_, Q_]:=And@@Not/@Q@@@Tuples[u, 2];
Select[Range[2, 100], !PrimeQ[#]&&stabstrQ[PrimePi/@First/@FactorInteger[#], CoprimeQ]&]
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CROSSREFS
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A200976 counts the partitions with these Heinz numbers.
A302696 is the pairwise coprime instead of pairwise non-coprime version.
A318717 counts pairwise intersecting strict partitions.
A328673 counts partitions with pairwise intersecting distinct parts, with Heinz numbers A328867 and restriction to triples A337599 (except n = 3).
Cf. A008578, A051185, A056239, A101268, A112798, A284825, A302569, A305843, A319752, A327516, A335236, A337666, A337667.
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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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