OFFSET
1,2
LINKS
Colin Barker, Table of n, a(n) for n = 1..850
EXAMPLE
a(3) = 810 because the first 3 10-gonal numbers are [1,10,27], and 3/(1/1+1/10+1/27) = 810/307.
MATHEMATICA
Module[{nn=20, pn}, pns=PolygonalNumber[10, Range[nn]]; Table[HarmonicMean[ Take[ pns, n]], {n, nn}]]//Numerator (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Nov 09 2017 *)
PROG
(PARI)
harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
s=vector(30); for(n=1, #s, s[n]=numerator(harmonicmean(vector(n, k, (8*k^2-6*k)/2)))); s
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
Colin Barker, Nov 25 2014
STATUS
approved