OFFSET
0,2
COMMENTS
See A239792 for references.
FORMULA
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)).
MAPLE
MATHEMATICA
b[n_] := b[n] = If[n < 1, 1, -Sum[Binomial[n - 1, k - 1] BernoulliB[k] b[n - k]/k, {k, 2, n}]/2];
a[n_] := b[2 n] // Denominator;
Table[a[n], {n, 0, 19}] (* Jean-François Alcover, Jun 28 2019 *)
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
Peter Luschny, Mar 26 2014
STATUS
approved