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 A250328 #14 Nov 06 2017 04:58:19
%S A250328 1,3,77,877,6271,36049,36423,422137,49691099,1448086909,11631128477,
%T A250328 2334008785,44471893747,1827784004699,832564679309,39202882860913,
%U A250328 196334425398149,3473612060358899,3478128507653999,205449856947685261,303604578504856471
%N A250328 Denominator of the harmonic mean of the first n pentagonal numbers.
%C A250328 a(n+1) is, for n >= 0, also the numerator of the partial sums of the reciprocals of twice the pentagonal numbers {A049450(k+1)}_{k>=0} with the denominators given in A294513(n) (assuming that A250327(n+1)/(n+1) = A294513(n)/2). - _Wolfdieter Lang_, Nov 02 2017
%H A250328 Colin Barker, <a href="/A250328/b250328.txt">Table of n, a(n) for n = 1..1000</a>
%e A250328 a(3) = 77 because the pentagonal numbers A000326(n), for n = 1,2,3 are 1, 5, 12 and 3/(1/1+1/5+1/12) = 180/77.
%t A250328 With[{s = Array[PolygonalNumber[5, #] &, 21]}, Denominator@ Array[HarmonicMean@ Take[s, #] &, Length@ s]] (* _Michael De Vlieger_, Nov 02 2017 *)
%o A250328 (PARI)
%o A250328 harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])
%o A250328 s=vector(30); for(k=1, #s, s[k]=denominator(harmonicmean(vector(k, i, (3*i^2-i)/2)))); s
%Y A250328 Cf. A000326, A250327 (numerators).
%K A250328 nonn,frac,easy
%O A250328 1,2
%A A250328 _Colin Barker_, Nov 18 2014