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

0, 1, 1, 3, 17, 31, 3, 5461, 257, 657, 6355, 60787, 12291, 22369621, 617093, 149943, 16843009, 5726623061, 71613, 91625968981, 162529435, 4870483401, 50991843607, 499069107643, 12129927891, 34118178995231, 5664905191661, 45148868444817, 165649641466501

Offset

0,4

Links

Table of n, a(n) for n=0..28.

Mathematica

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

Prog

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

Crossrefs

Cf. A001469.

Sequence in context: A188620 A152529 A126782 * A031024 A365234 A377175

Adjacent sequences: A090645 A090646 A090647 * A090649 A090650 A090651

Keyword

nonn

Author

Benoit Cloitre, Dec 13 2003

Extensions

Corrected and extended by Harvey P. Dale, Jul 20 2011

Status

approved