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 A239793 #12 Jun 28 2019 07:14:55
%S A239793 1,24,320,10752,184320,360448,23855104,94371840,285212672,
%T A239793 267764367360,3720515420160,987842478080,201004469452800,
%U A239793 103903848824832,637716744110080,11997870882291712,368450744514248704,2251799813685248,164633587978155851776,9367487224930631680
%N A239793 Denominator of b_{2n}(1/4), where b_{n}(x) are Nörlund's generalized Bernoulli polynomials.
%C A239793 See A239792 for references.
%F A239793 Let b(n) = -sum_{2<=k<=n}(C(n-1, k-1)*Bernoulli(k)*b(n-k)/k)/2 for n>0 and otherwise 1. Then a(n) = denominator(b(2*n)).
%p A239793 b := proc(n) option remember; if n < 1 then 1 else
%p A239793 -add(binomial(n-1, k-1)*bernoulli(k)*b(n-k)/k, k= 2..n)/2 fi end:
%p A239793 A239793 := n -> denom(b(2*n));
%p A239793 seq(A239793(n), n=0..19);
%t A239793 b[n_] := b[n] = If[n < 1, 1, -Sum[Binomial[n - 1, k - 1] BernoulliB[k] b[n - k]/k, {k, 2, n}]/2];
%t A239793 a[n_] := b[2 n] // Denominator;
%t A239793 Table[a[n], {n, 0, 19}] (* _Jean-François Alcover_, Jun 28 2019 *)
%Y A239793 Cf. A220412, A239792 (numerators).
%K A239793 nonn,frac
%O A239793 0,2
%A A239793 _Peter Luschny_, Mar 26 2014