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A197116 Number of k such that (2^k-1)*2^n-1 is prime with 0 < k < n+1. 4
0, 2, 2, 2, 4, 1, 3, 1, 2, 2, 5, 1, 4, 2, 1, 2, 4, 3, 3, 1, 2, 1, 4, 1, 1, 1, 0, 2, 3, 1, 6, 1, 3, 1, 2, 3, 3, 3, 3, 1, 7, 3, 2, 1, 4, 2, 3, 1, 3, 1, 2, 2, 3, 1, 4, 3, 3, 1, 3, 0, 4, 0, 3, 3, 3, 2, 1, 2, 0, 3, 1, 2, 4, 4, 3, 1, 4, 2, 3, 3, 3, 2, 3, 6, 0, 4, 4, 2, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

As n increases sum of a(n) from 1 to n / n tends to 2.66.

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..3000

PROG

(PARI) a(n) = {nb = 0; for (k=1, n, if (isprime((2^k-1)*2^n-1), nb++); ); return (nb); } \\ Michel Marcus, Mar 07 2013

CROSSREFS

Cf. A197117, A197118, A197119.

Sequence in context: A346801 A326375 A071470 * A104461 A308042 A335694

Adjacent sequences:  A197113 A197114 A197115 * A197117 A197118 A197119

KEYWORD

nonn

AUTHOR

Pierre CAMI, Oct 11 2011

STATUS

approved

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Last modified October 5 03:25 EDT 2022. Contains 357240 sequences. (Running on oeis4.)