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 A164020 #24 Feb 16 2025 08:33:11
%S A164020 1,2,6,4,30,6,42,8,30,10,66,12,2730,14,6,16,510,18,798,20,330,22,138,
%T A164020 24,2730,26,6,28,870,30,14322,32,510,34,6,36,1919190,38,6,40,13530,42,
%U A164020 1806,44,690,46,282,48,46410,50,66,52,1590,54,798,56,870,58,354,60,56786730
%N A164020 Denominators of Bernoulli numbers interleaved with even numbers.
%H A164020 G. C. Greubel, <a href="/A164020/b164020.txt">Table of n, a(n) for n = 0..1000</a>
%H A164020 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BernoulliNumber.html">Bernoulli Number</a>
%F A164020 a(2*n) = A002445(n).
%F A164020 a(2*n+1) = 2*(n+1).
%F A164020 a(n) divides A057643(n). _Franklin T. Adams-Watters_, Aug 03 2012
%t A164020 a[n_]:=If[OddQ[n], n+1, BernoulliB[n] // Denominator]; Table[a[n], {n, 0, 60}](* _Jean-François Alcover_, Dec 29 2012 *)
%t A164020 With[{nn=60},Riffle[Denominator[BernoulliB[Range[0,nn,2]]],Range[2,nn,2]]] (* _Harvey P. Dale_, Jul 18 2015 *)
%o A164020 (Magma) [IsEven(n) select Denominator(Bernoulli(n)) else n+1: n in [0..100]]; // _Vincenzo Librandi_, Sep 08 2017
%Y A164020 Cf. A027642, A141056, A160014.
%K A164020 nonn
%O A164020 0,2
%A A164020 _Paul Curtz_, Aug 08 2009
%E A164020 Extended by _R. J. Mathar_, Sep 23 2009