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 A223037 a(n) = largest prime p such that Sum_{primes q = 2, ..., p} 1/q does not exceed n. 2
 3, 271, 5195969, 1801241230056600467 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Since Sum_{prime q} 1/q diverges, the sequence is infinite. In fact, by the Prime Number Theorem Prime(k) ~ k log k as k -> infinity, and by integration Sum_{k <= n} 1/(k log k) ~ log log n, so a(n) ~ Prime(Floor(e^e^n)). a(4) = A000040(A046024(4)-1) = Prime, but Mathematica 7.0.0 cannot compute this prime on a Mac computer running OS X. Instead, using a(4) = largest prime < A016088(4) = 1801241230056600523, Mathematica's PrimeQ function finds that a(4) = 1801241230056600467. See A016088 for other relevant comments, references, links, and programs. LINKS FORMULA a(n) = A000040(A046024(n)-1) = largest prime < A016088(n). a(n) ~ Prime(Floor(e^e^n)) = A000040(A096232(n)) as n -> infinity. EXAMPLE a(1) = 3 because 1/2 + 1/3 < 1 < 1/2 + 1/3 + 1/5. CROSSREFS Cf. A016088, A046024, A024451, A096232. Sequence in context: A230373 A003761 A216471 * A171358 A115477 A051365 Adjacent sequences:  A223034 A223035 A223036 * A223038 A223039 A223040 KEYWORD nonn,hard,more AUTHOR Jonathan Sondow, Apr 16 2013 STATUS approved

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Last modified November 18 14:55 EST 2019. Contains 329262 sequences. (Running on oeis4.)