This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A250550 #8 Nov 09 2017 15:16:08
%S A250550 1,20,810,28080,596700,5012280,29238300,1938081600,7994586600,
%T A250550 328666338000,14822851843800,48511151488800,367876232123400,
%U A250550 20997243402735600,427443883555689000,55624697380046995200,59101240966299932400,479763014902905333600
%N A250550 Numerator of the harmonic mean of the first n 10-gonal numbers.
%H A250550 Colin Barker, <a href="/A250550/b250550.txt">Table of n, a(n) for n = 1..850</a>
%e A250550 a(3) = 810 because the first 3 10-gonal numbers are [1,10,27], and 3/(1/1+1/10+1/27) = 810/307.
%t A250550 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 *)
%o A250550 (PARI)
%o A250550 harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
%o A250550 s=vector(30); for(n=1, #s, s[n]=numerator(harmonicmean(vector(n, k, (8*k^2-6*k)/2)))); s
%Y A250550 Cf. A001107 (10-gonal numbers), A250551 (denominators).
%K A250550 nonn,frac
%O A250550 1,2
%A A250550 _Colin Barker_, Nov 25 2014