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 A051721 #19 Jul 02 2025 16:01:58
%S A051721 4,5,15,35,105,105,105,165,165,455,15015,1365,1365,255,255,11305,
%T A051721 33915,21945,21945,345,3795,10465,31395,1365,1365,435,435,346115,
%U A051721 1038345,55335,608685,255,255,319865,959595,959595,959595,6765,6765,61705
%N A051721 Denominators of column 3 of table described in A051714/A051715.
%H A051721 Seiichi Manyama, <a href="/A051721/b051721.txt">Table of n, a(n) for n = 0..1000</a>
%H A051721 M. Kaneko, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/KANEKO/AT-kaneko.html">The Akiyama-Tanigawa algorithm for Bernoulli numbers</a>, J. Integer Sequences, 3 (2000), #00.2.9.
%t A051721 a[0, k_] := 1/(k+1); a[n_, k_] := a[n, k] = (k+1)*(a[n-1, k] - a[n-1, k+1]); a[n_] := a[n, 3] // Denominator; Table[a[n], {n, 0, 39}] (* _Jean-François Alcover_, Sep 17 2012 *)
%Y A051721 Cf. A051720.
%K A051721 nonn,easy,nice
%O A051721 0,1
%A A051721 _N. J. A. Sloane_
%E A051721 More terms from _James Sellers_, Dec 08 1999