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%I #8 Jun 01 2022 20:31:09
%S 1,5,180,2640,23100,157080,183260,2408560,317026710,10215305100,
%T 89894684880,19613385792,403708857552,17825298787296,8681152006800,
%U 435215087274240,2312080151144400,43249499297877600,45652249258870800,2835244953971976000,4394629678656562800
%N Numerator of the harmonic mean of the first n pentagonal numbers.
%H Colin Barker, <a href="/A250327/b250327.txt">Table of n, a(n) for n = 1..1000</a>
%e a(3) = 180 because the first 3 pentagonal numbers are [1,5,12] and 3/(1/1+1/5+1/12) = 180/77.
%t Table[Numerator[n/Total[1/PolygonalNumber[5,Range[n]]]],{n,30}] (* _Harvey P. Dale_, Jun 01 2022 *)
%o (PARI)
%o harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
%o s=vector(30); for(k=1, #s, s[k]=numerator(harmonicmean(vector(k, i, (3*i^2-i)/2)))); s
%Y Cf. A250328 (denominators).
%K nonn
%O 1,2
%A _Colin Barker_, Nov 18 2014
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