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 A250133 Denominator of the harmonic mean of the first n composite numbers. 11
 1, 5, 13, 47, 271, 301, 2287, 491, 1045, 367, 1919, 1999, 22829, 23599, 121691, 1628183, 15054047, 15440147, 15800507, 32276689, 32931889, 570652913, 83022119, 84480719, 1631388461, 1656970061, 1681912121, 11939665247, 12098387447, 12253582487, 285324285601 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numerator of the sum of the reciprocals of the first n composite numbers (A250133/A296358). LINKS Colin Barker, Table of n, a(n) for n = 1..500 EXAMPLE a(3) = 13 because the first 3 composite numbers are [4,6,8] and 3 / (1/4+1/6+1/8) = 72/13. 1/4, 5/12, 13/24, 47/72, 271/360, 301/360, 2287/2520, 491/504, 1045/1008, 367/336, 1919/1680, 1999/1680, 22829/18480, ... = A250133/A296358 PROG (PARI) harmonicmean(v) = #v / sum(k=1, #v, 1/v[k]) composite(n) = for(k=0, primepi(n), isprime(n++)&&k--); n \\ from A002808 s=vector(100); for(k=1, #s, s[k]=denominator(harmonicmean(vector(k, i, composite(i))))); s CROSSREFS Cf. A250132 (numerators). The following fractions are all related to each other: Sum 1/n: A001008/A002805, Sum 1/prime(n): A024451/A002110 and A106830/A034386, Sum 1/nonprime(n): A282511/A282512, Sum 1/composite(n): A250133/A296358. Sequence in context: A304964 A120790 A162563 * A025545 A146152 A082132 Adjacent sequences:  A250130 A250131 A250132 * A250134 A250135 A250136 KEYWORD nonn AUTHOR Colin Barker, Nov 14 2014 STATUS approved

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Last modified January 18 23:05 EST 2019. Contains 319282 sequences. (Running on oeis4.)