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Search: id:A085770
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| A085770 |
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Number of odd semiprimes < 10^n. Number of terms of A046315 < 10^n. |
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+0
1
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| 1, 19, 204, 1956, 18245, 168497, 1555811, 14426124, 134432669, 1258822220, 11840335764, 111817881036, 1059796387004, 10076978543513
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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a(1)=1 because A046315(1)=9=3*3 is the only odd semiprime < 10^1,
a(2)=19 because there are 19 terms of A046315 < 10^2.
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MATHEMATICA
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OddSemiPrimePi[n_] := Sum[ PrimePi[n/Prime@i], {i, 2, PrimePi@Sqrt@n}] - Binomial[PrimePi@Sqrt@n, 2]; Table[OddSemiPrimePi[10^n], {n, 14}] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A046315 (odd numbers divisible by exactly 2 primes), A066265 (number of semiprimes < 10^n).
Sequence in context: A160452 A113596 A155670 this_sequence A002501 A125407 A023017
Adjacent sequences: A085767 A085768 A085769 this_sequence A085771 A085772 A085773
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KEYWORD
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more,nonn
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AUTHOR
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Hugo Pfoertner (hugo(AT)pfoertner.org), Jul 22 2003
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EXTENSIONS
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a(10)-a(14) from Robert G. Wilson v (rgwv(at)rgwv.com), Feb 02 2006
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