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A090648 a(n)=2*(4^n-1)/denominator(B(2n)) where B(k) denotes the k-th Bernoulli number. 1

%I

%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

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Last modified October 23 21:27 EDT 2021. Contains 348217 sequences. (Running on oeis4.)