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 A326580 #14 Jul 31 2021 20:14:01
%S A326580 1,6,30,42,90,66,2730,30,510,798,2310,138,13650,54,870,14322,5610,210,
%T A326580 1919190,78,13530,1806,2070,282,324870,1122,1590,43890,16530,354,
%U A326580 56786730,126,6630,64722,690,4686,140100870,150,2310,3318,6210270,498,57873270,174
%N A326580 a(n) = (2*n+1)*denominator((2*n+1)*Bernoulli(2*n)).
%H A326580 Robert Israel, <a href="/A326580/b326580.txt">Table of n, a(n) for n = 0..10000</a>
%F A326580 a(n) = A326579(2*n + 1).
%p A326580 A326580 := n -> (2*n+1)*denom((2*n+1)*bernoulli(2*n)):
%p A326580 seq(A326580(n), n=0..43);
%t A326580 Table[(2n+1)Denominator[(2n+1)BernoulliB[2n]],{n,0,50}] (* _Harvey P. Dale_, Jul 31 2021 *)
%o A326580 (PARI) a(n) = (2*n+1)*denominator((2*n+1)*bernfrac(2*n)); \\ _Michel Marcus_, Jul 19 2019
%Y A326580 Cf. A326579, A326578, A326478, A027641/A027642 (Bernoulli).
%K A326580 nonn
%O A326580 0,2
%A A326580 _Peter Luschny_, Jul 17 2019