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 A085770 Number of odd semiprimes < 10^n. Number of terms of A046315 < 10^n. 2
 0, 1, 19, 204, 1956, 18245, 168497, 1555811, 14426124, 134432669, 1258822220, 11840335764, 111817881036, 1059796387004, 10076978543513, 96091983644261, 918679875630905, 8803388145953381, 84537081118605467, 813340036541900706, 7838825925851034479, 75669246175972479567 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = A066265(n) - A220262(n) for n > 1. - Jinyuan Wang, Jul 30 2021 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), A220262, A292785. Sequence in context: A160452 A113596 A155670 * A002501 A180364 A125407 Adjacent sequences: A085767 A085768 A085769 * A085771 A085772 A085773 KEYWORD 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 a(0) inserted by and a(17)-a(21) from Jinyuan Wang, Jul 30 2021 STATUS approved

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Last modified February 6 21:39 EST 2023. Contains 360111 sequences. (Running on oeis4.)