%I #15 Jul 28 2015 12:50:06

%S 0,1,1,3,17,31,3,5461,257,657,6355,60787,12291,22369621,617093,149943,

%T 16843009,5726623061,71613,91625968981,162529435,4870483401,

%U 50991843607,499069107643,12129927891,34118178995231,5664905191661,45148868444817,165649641466501

%N a(n)=2*(4^n-1)/denominator(B(2n)) where B(k) denotes the k-th Bernoulli number.

%t Table[(2*(4^n-1))/Denominator[BernoulliB[2n]],{n,0,40}] (* _Harvey P. Dale_, Jul 20 2011 *)

%o (PARI) a(n)=2*(4^n-1)/denominator(bernfrac(2*n))

%Y Cf. A001469.

%K nonn

%O 0,4

%A _Benoit Cloitre_, Dec 13 2003

%E Corrected and extended by _Harvey P. Dale_, Jul 20 2011