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A338911
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Numbers of the form prime(x) * prime(y) where x and y are both even.
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14
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9, 21, 39, 49, 57, 87, 91, 111, 129, 133, 159, 169, 183, 203, 213, 237, 247, 259, 267, 301, 303, 321, 339, 361, 371, 377, 393, 417, 427, 453, 481, 489, 497, 519, 543, 551, 553, 559, 579, 597, 623, 669, 687, 689, 703, 707, 717, 749, 753, 789, 791, 793, 813, 817
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OFFSET
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1,1
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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} 237: {2,22} 481: {6,12}
21: {2,4} 247: {6,8} 489: {2,38}
39: {2,6} 259: {4,12} 497: {4,20}
49: {4,4} 267: {2,24} 519: {2,40}
57: {2,8} 301: {4,14} 543: {2,42}
87: {2,10} 303: {2,26} 551: {8,10}
91: {4,6} 321: {2,28} 553: {4,22}
111: {2,12} 339: {2,30} 559: {6,14}
129: {2,14} 361: {8,8} 579: {2,44}
133: {4,8} 371: {4,16} 597: {2,46}
159: {2,16} 377: {6,10} 623: {4,24}
169: {6,6} 393: {2,32} 669: {2,48}
183: {2,18} 417: {2,34} 687: {2,50}
203: {4,10} 427: {4,18} 689: {6,16}
213: {2,20} 453: {2,36} 703: {8,12}
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MAPLE
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q:= n-> (l-> add(i[2], i=l)=2 and andmap(i->
numtheory[pi](i[1])::even, l))(ifactors(n)[2]):
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MATHEMATICA
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Select[Range[100], PrimeOmega[#]==2&&OddQ[Times@@(1+PrimePi/@First/@FactorInteger[#])]&]
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CROSSREFS
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A338910 is the odd instead of even version.
A001221 counts distinct prime indices.
A300912 lists semiprimes with relatively prime indices.
A318990 lists semiprimes with divisible indices.
A338904 groups semiprimes by weight.
A338909 lists semiprimes with non-relatively prime indices.
Cf. A005117, A037143, A055684, A056239, A065516, A112798, A128301, A195017, A320655, A320732, A320892, A338898, A339002, A339003.
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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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