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A146168
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Number of odd squarefree semiprimes (A036388) < 2^n.
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2
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0, 0, 0, 1, 2, 8, 20, 46, 96, 197, 404, 798, 1599, 3134, 6169, 12093, 23640, 46199, 90180, 176198, 343927, 671783, 1312304, 2564485, 5012807, 9803883, 19181677, 37545265, 73524262, 144038812, 282313035, 553557959, 1085860455
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OFFSET
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1,5
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LINKS
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FORMULA
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EXAMPLE
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a(5)= 2. The semiprimes less than 2^5 are 15 and 21. Formula gives 10-pi(5)-pi(2^4)+1 = 2.
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MATHEMATICA
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Table[lim=2^n; Sum[PrimePi[lim/p]-PrimePi[p], {p, Prime[Range[2, PrimePi[Sqrt[lim]]]]}], {n, 20}]
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CROSSREFS
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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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