A197118 - OEIS

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A197118

Number of k such that (2^k+1)*2^n-1 is prime with 0 < k < n+1.

1, 2, 2, 3, 0, 4, 2, 3, 1, 4, 1, 4, 2, 1, 2, 5, 0, 5, 1, 2, 2, 4, 2, 4, 1, 3, 0, 6, 2, 4, 0, 4, 1, 3, 3, 4, 1, 4, 3, 2, 0, 5, 7, 1, 0, 5, 1, 5, 0, 1, 3, 7, 2, 8, 3, 4, 1, 4, 2, 8, 0, 3, 5, 6, 0, 7, 2, 2, 1, 1, 2, 8, 1, 2, 1, 7, 0, 2, 0, 3, 0, 5, 0, 4, 1, 2, 2, 6, 1, 4

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OFFSET

1,2

COMMENTS

As n increases sum 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) = sum(k=1, n, isprime((2^k+1)*2^n-1)); \\ Michel Marcus, Sep 21 2019

CROSSREFS

Cf. A197116, A197117, A197119.

Sequence in context: A071448 A071449 A035189 * A035143 A035173 A263254

Adjacent sequences: A197115 A197116 A197117 * A197119 A197120 A197121

KEYWORD

nonn

AUTHOR

Pierre CAMI, Oct 11 2011

STATUS

approved