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 A146167 Number of odd squarefree semiprimes (A046388) <= n. 0
 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,21 LINKS FORMULA a(n) = A072000(n) - A000720(floor(sqrt(n))) - A000720(floor(n/2)) + 1. EXAMPLE a(33)= 3. The semiprimes <=33 are 15, 21 and 33. Formula gives 11-pi(5)-pi(16)+1 = 3. MATHEMATICA Accumulate[Table[If[OddQ[n]&&SquareFreeQ[n]&&PrimeOmega[n]==2, 1, 0], {n, 0, 100}]] (* Harvey P. Dale, Feb 08 2016 *) CROSSREFS Cf. A046388, A001358 (semiprimes), A072000 (Number of semiprimes <= n), A000720 (pi(n), the number of primes <= n). Sequence in context: A279758 A082996 A094382 * A103380 A309120 A098708 Adjacent sequences:  A146164 A146165 A146166 * A146168 A146169 A146170 KEYWORD nonn AUTHOR Washington Bomfim, Oct 27 2008 STATUS approved

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Last modified January 19 03:54 EST 2020. Contains 331031 sequences. (Running on oeis4.)