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 A203967 The number of positive integers <= n that have a prime number of divisors. 4
 0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 9, 10, 10, 11, 11, 11, 11, 12, 12, 13, 13, 13, 13, 14, 14, 15, 15, 15, 15, 15, 15, 16, 16, 16, 16, 17, 17, 18, 18, 18, 18, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 21, 21, 22, 22, 23, 23, 23, 24, 24, 24, 25, 25, 25 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) = a(n-1) + A010055(n) * A010051(A100995(n)+1). - Reinhard Zumkeller, Jun 06 2013 MATHEMATICA Table[Total[Table[PrimePi[m^(1/n)], {n, Table[Prime[n]-1, {n, 1, 20}]}]], {m, 1, 100}] tot = 0; Table[If[PrimeQ[DivisorSigma[0, n]], tot++]; tot, {n, 100}] (* T. D. Noe, Jan 10 2012 *) PROG (Haskell) a203967 n = length \$ takeWhile (<= n) a009087_list -- Reinhard Zumkeller, Jun 06 2013 CROSSREFS Cf. A009087. Sequence in context: A047784 A047742 A302778 * A267530 A050292 A181627 Adjacent sequences:  A203964 A203965 A203966 * A203968 A203969 A203970 KEYWORD nonn AUTHOR Geoffrey Critzer, Jan 08 2012 STATUS approved

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Last modified June 19 05:33 EDT 2019. Contains 324218 sequences. (Running on oeis4.)