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 A220411 #10 Jun 27 2019 08:38:53
%S A220411 1,-6,60,-504,2160,-3168,786240,-51840,1762560,-82736640,1437004800,
%T A220411 -858470400,101896704000,-1881169920,8659353600,-855305256960,
%U A220411 14071151001600,-150493593600,8252165711462400,-70431001804800,24434139856896000,-1076294062964736000
%N A220411 The denominators of J. L. Fields generalized Bernoulli polynomials.
%C A220411 See A220412 for definitions and references.
%t A220411 F[0, _] = 1; F[n_, x_] := F[n, x] = -2x Sum[Binomial[n-1, 2k+1] BernoulliB[2k+2]/(2k+2) F[n-2k-2, x], {k, 0, n/2-1}] // Expand;
%t A220411 a[n_] := (-1)^n Denominator[Together[F[2n, x]]];
%t A220411 Table[a[n], {n, 0, 21}] (* _Jean-François Alcover_, Jun 27 2019 *)
%K A220411 sign
%O A220411 0,2
%A A220411 _Peter Luschny_, Dec 30 2012