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A250549 Denominator of the harmonic mean of the first n 9-gonal numbers. 2
1, 5, 83, 1945, 49177, 1833349, 141933773, 2422703191, 23493728113, 306193780933, 920490263449, 72844719575371, 3136916685865153, 97366698355411543, 487364191723246127, 26098860817171249607, 496295891513328449033, 1821113866092559163621 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
EXAMPLE
a(3) = 83 because the first 3 9-gonal numbers are [1,9,24], and 3/(1/1+1/9+1/24) = 216/83.
MATHEMATICA
Module[{nn=20, p9}, p9=PolygonalNumber[9, Range[nn]]; Table[Denominator[ HarmonicMean[ Take[p9, n]]], {n, nn}]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 26 2019 *)
PROG
(PARI)
harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
s=vector(30); for(n=1, #s, s[n]=denominator(harmonicmean(vector(n, k, (7*k^2-5*k)/2)))); s
CROSSREFS
Cf. A001106 (9-gonal numbers), A250548 (numerators).
Sequence in context: A173876 A368080 A348791 * A035512 A054953 A215172
KEYWORD
nonn,frac
AUTHOR
Colin Barker, Nov 25 2014
STATUS
approved

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Last modified April 22 01:34 EDT 2024. Contains 371887 sequences. (Running on oeis4.)