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A339362
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Sum of prime indices of the n-th squarefree semiprime.
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7
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3, 4, 5, 5, 6, 6, 7, 7, 8, 7, 9, 8, 10, 9, 8, 10, 11, 12, 9, 11, 13, 9, 14, 10, 15, 12, 10, 13, 16, 11, 17, 14, 12, 18, 11, 19, 15, 16, 12, 20, 17, 21, 11, 13, 22, 14, 23, 18, 13, 24, 19, 25, 20, 15, 12, 26, 21, 27, 14, 16, 28, 13, 22, 29, 17, 15, 30, 23, 13
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OFFSET
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1,1
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COMMENTS
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A squarefree semiprime (A006881) is a product of any two distinct prime numbers. A prime index of n is a number m such that the m-th prime number divides n. The multiset of prime indices of n is row n of A112798.
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LINKS
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FORMULA
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EXAMPLE
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The sequence of all squarefree semiprimes together with the sums of their prime indices begins:
6: 1 + 2 = 3
10: 1 + 3 = 4
14: 1 + 4 = 5
15: 2 + 3 = 5
21: 2 + 4 = 6
22: 1 + 5 = 6
26: 1 + 6 = 7
33: 2 + 5 = 7
34: 1 + 7 = 8
35: 3 + 4 = 7
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MATHEMATICA
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Table[Plus@@PrimePi/@First/@FactorInteger[n], {n, Select[Range[100], SquareFreeQ[#]&&PrimeOmega[#]==2&]}]
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CROSSREFS
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A003963 gives the product of prime indices of n.
A006881 lists squarefree semiprimes.
A025129 gives the sum of squarefree semiprimes of weight n.
A056239 (weight) gives the sum of prime indices of n.
A332765/A339114 give the greatest/least squarefree semiprime of weight n.
A338904 groups semiprimes by weight.
A338905 groups squarefree semiprimes by weight.
A339116 groups squarefree semiprimes by greater prime factor.
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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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