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 A250344 #6 Nov 19 2014 10:28:22 %S A250344 1,12,90,1680,6300,83160,1261260,576576,11027016,1163962800, %T A250344 1280359080,32125373280,174012438600,80313433200,2495453103000, %U A250344 165032631878400,175347171370800,1299631976042400,50757848842100400,53429314570632000,2300131992265707600 %N A250344 Numerator of the harmonic mean of the first n hexagonal numbers. %H A250344 Colin Barker, <a href="/A250344/b250344.txt">Table of n, a(n) for n = 1..1000</a> %e A250344 a(3) = 90 because the first 3 hexagonal numbers are [1,6,15], and 3/(1/1+1/6+1/15) = 90/37. %o A250344 (PARI) %o A250344 harmonicmean(v) = #v / sum(k=1, #v, 1/v[k]) %o A250344 s=vector(30); for(n=1, #s, s[n]=numerator(harmonicmean(vector(n, k, k*(2*k-1))))); s %Y A250344 Cf. A000384 (hexagonal numbers), A082687 (denominators). %K A250344 nonn %O A250344 1,2 %A A250344 _Colin Barker_, Nov 19 2014