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%I #21 Aug 11 2023 13:47:06
%S 0,1,19,204,1956,18245,168497,1555811,14426124,134432669,1258822220,
%T 11840335764,111817881036,1059796387004,10076978543513,96091983644261,
%U 918679875630905,8803388145953381,84537081118605467,813340036541900706,7838825925851034479,75669246175972479567
%N Number of odd semiprimes < 10^n. Number of terms of A046315 < 10^n.
%F a(n) = A066265(n) - A220262(n) for n > 1. - _Jinyuan Wang_, Jul 30 2021
%e a(1)=1 because A046315(1)=9=3*3 is the only odd semiprime < 10^1,
%e a(2)=19 because there are 19 terms of A046315 < 10^2.
%t OddSemiPrimePi[n_] := Sum[ PrimePi[n/Prime@i] - i + 1, {i, 2, PrimePi@ Sqrt@ n}]; Table[ OddSemiPrimePi[10^n], {n, 14}] (* _Robert G. Wilson v_, Feb 02 2006 *)
%Y Cf. A046315 (odd numbers divisible by exactly 2 primes), A066265 (number of semiprimes < 10^n), A220262, A292785.
%K nonn
%O 0,3
%A _Hugo Pfoertner_, Jul 22 2003
%E a(10)-a(14) from _Robert G. Wilson v_, Feb 02 2006
%E a(15)-a(16) from _Donovan Johnson_, Mar 18 2010
%E a(0) inserted by and a(17)-a(21) from _Jinyuan Wang_, Jul 30 2021
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