1,3

Supposedly the difference from A101050 is that the k here are required to be strictly positive (nonzero positive). - R. J. Mathar, Dec 13 2008

Pierre CAMI and Robert G. Wilson v, Table of n, a(n) for n = 1..119.

f[n_] := Block[{k = 1, p = Prime@n}, While[ !PrimeQ[p*2^k - 1], k++ ]; k]; Array[f, 97]

Cf. A000040, A126715.

Sequence in context: A055095 A048685 A101050 * A190167 A171565 A328266

Adjacent sequences: A128976 A128977 A128978 * A128980 A128981 A128982

nonn

Pierre CAMI and Robert G. Wilson v, Feb 16 2007

approved