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%I #26 Sep 06 2024 14:08:32
%S 0,0,0,1,2,8,20,46,96,197,404,798,1599,3134,6169,12093,23640,46199,
%T 90180,176198,343927,671783,1312304,2564485,5012807,9803883,19181677,
%U 37545265,73524262,144038812,282313035,553557959,1085860455,2130904274,4183364732,8215861037
%N Number of odd squarefree semiprimes (A046388) < 2^n.
%H Amiram Eldar, <a href="/A146168/b146168.txt">Table of n, a(n) for n = 1..57</a> (calculated using the b-files at A060967, A007053 and A125527)
%F a(n) = A125527(n) - A060967(n) - A007053(n-1) + 1, for n > 1.
%e a(5) = 2. The odd squarefree semiprimes less than 2^5 are 15 and 21. The formula gives 10 - pi(5) - pi(2^4) + 1 = 2.
%t Table[lim=2^n; Sum[PrimePi[lim/p]-PrimePi[p], {p, Prime[Range[2,PrimePi[Sqrt[lim]]]]}], {n,20}]
%Y Cf. A046388, A001358 (semiprimes), A000720 (pi(n), the number of primes <= n), A007053 (number of primes <= 2^n), A060967, A125527 (number of semiprimes <= 2^n).
%K nonn
%O 1,5
%A _Washington Bomfim_, Oct 27 2008
%E a(34) onwards from _Amiram Eldar_, Sep 05 2024