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 A073799 Numbers that begin a run of consecutive integers k such that PrimePi(k) divides 2^k. 2
 2, 7, 19, 53, 131, 311, 719, 1619, 3671, 8161, 17863, 38873, 84017, 180503, 386093, 821641, 1742537, 3681131 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It seems that each term is a bit larger than twice the previous one. Runs have lengths 3, 4, 4, 6, 6, 2, 8, 2, 2, 6, 18, 18, 30, 8, 24, 6, 2, 18, ..., respectively. LINKS FORMULA Solutions to 2^(x-1) mod PrimePi(x-1) > 0 but 2^x mod PrimePi(x) = 0. MATHEMATICA aQ[k_] := Divisible[2^k, PrimePi[k]]; s = {}; len = {}; n = 2; While[Length[s] < 10, While[! aQ[n], n++]; n1 = n; While[aQ[n], n++]; If[n > n1, AppendTo[s, n1]; AppendTo[len, n - n1]]; n++]; s (* Amiram Eldar, Dec 11 2018 *) CROSSREFS Cf. A000079, A000720, A015910, A062173, A064367, A073797, A073798. Cf. A033844. - R. J. Mathar, Sep 23 2008 Sequence in context: A099484 A018030 A051354 * A040016 A145519 A030224 Adjacent sequences:  A073796 A073797 A073798 * A073800 A073801 A073802 KEYWORD nonn,more AUTHOR Labos Elemer, Aug 12 2002 EXTENSIONS Edited by Jon E. Schoenfield, Dec 10 2018 a(15)-a(18) from Amiram Eldar, Dec 11 2018 STATUS approved

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Last modified January 18 05:30 EST 2019. Contains 319269 sequences. (Running on oeis4.)