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 A294521 #9 Nov 16 2017 12:14:37
%S A294521 1,12,44,704,73920,320320,9929920,89369280,3664140480,84275231040,
%T A294521 1432678927680,1432678927680,87393414588480,87393414588480,
%U A294521 6204932435782080,14736714534982440,132630430814841960,5703108525038204280,5703108525038204280,18249947280122253696,1843244675292347623296
%N A294521 Denominators of the partial sums of the reciprocals of the dodecagonal numbers (k + 1)*(5*k + 1) = A051624(k+1), for k >= 0.
%C A294521 The corresponding numerators are given in A294520. Details are found there.
%F A294521 a(n) = denominator(V(5,1;n)) with V(5,1;n) = Sum_{k=0..n} 1/((k + 1)*(5*k + 1)) = Sum_{k=0..n} 1/A051624(k+1) = (1/4)*Sum_{k=0..n} (1/(k + 1/5) - 1/(k+1)). For the formula in terms of the digamma function see A294520.
%e A294521 See A294520 for the rationals.
%o A294521 (PARI) a(n) = denominator(sum(k=0, n, 1/((k + 1)*(5*k + 1)))); \\ _Michel Marcus_, Nov 15 2017
%Y A294521 Cf. A294520.
%K A294521 nonn,frac,easy
%O A294521 0,2
%A A294521 _Wolfdieter Lang_, Nov 15 2017