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A250132
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Numerator of the harmonic mean of the first n composite numbers.
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2
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4, 24, 72, 288, 1800, 2160, 17640, 4032, 9072, 3360, 18480, 20160, 240240, 258720, 1386000, 19219200, 183783600, 194594400, 205405200, 432432000, 454053600, 8086478400, 1207720800, 1260230400, 24942060000, 25939742400, 26937424800, 195545750400, 202529527200
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(3) = 72 because the first 3 composite numbers are [4,6,8] and 3 / (1/4+1/6+1/8) = 72/13.
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MATHEMATICA
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Module[{comps=Select[Range[50], CompositeQ], len}, len=Length[comps]; Table[ HarmonicMean[ Take[comps, n]], {n, len}]]//Numerator (* Harvey P. Dale, Jun 30 2017 *)
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PROG
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(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]=numerator(harmonicmean(vector(k, i, composite(i))))); s
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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