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 A085770 Number of odd semiprimes < 10^n. Number of terms of A046315 < 10^n. 2
 1, 19, 204, 1956, 18245, 168497, 1555811, 14426124, 134432669, 1258822220, 11840335764, 111817881036, 1059796387004, 10076978543513, 96091983644261, 918679875630905 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE 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. MATHEMATICA OddSemiPrimePi[n_] := Sum[ PrimePi[n/Prime@i] - i + 1, {i, 2, PrimePi@ Sqrt@ n}]; Table[ OddSemiPrimePi[10^n], {n, 14}] (* Robert G. Wilson v *) CROSSREFS Cf. A046315 (odd numbers divisible by exactly 2 primes), A066265 (number of semiprimes < 10^n), A292785. Sequence in context: A160452 A113596 A155670 * A002501 A180364 A125407 Adjacent sequences:  A085767 A085768 A085769 * A085771 A085772 A085773 KEYWORD more,nonn AUTHOR Hugo Pfoertner, Jul 22 2003 EXTENSIONS a(10)-a(14) from Robert G. Wilson v, Feb 02 2006 a(15)-a(16) from Donovan Johnson, Mar 18 2010 STATUS approved

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Last modified April 11 22:01 EDT 2021. Contains 342888 sequences. (Running on oeis4.)