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A197117 Number of k such that (2^k-1)*2^n+1 is prime with 0 < k < n+1. 4
1, 2, 0, 3, 1, 2, 0, 3, 2, 2, 0, 3, 1, 4, 0, 3, 2, 5, 2, 4, 2, 1, 1, 2, 3, 2, 1, 2, 2, 3, 0, 4, 2, 4, 1, 2, 4, 7, 0, 4, 3, 3, 0, 4, 5, 1, 0, 3, 2, 2, 1, 1, 2, 2, 0, 2, 3, 2, 1, 4, 0, 5, 0, 2, 5, 4, 0, 7, 4, 2, 2, 7, 0, 3, 1, 2, 0, 5, 0, 2, 3, 1, 0, 4, 4, 0, 0, 1, 0, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

As n increases sum a(n) from n=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, A197118, A197119.

Sequence in context: A078804 A071465 A333409 * A343879 A275387 A051709

Adjacent sequences:  A197114 A197115 A197116 * A197118 A197119 A197120

KEYWORD

nonn

AUTHOR

Pierre CAMI, Oct 11 2011

STATUS

approved

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Last modified September 30 17:27 EDT 2022. Contains 357106 sequences. (Running on oeis4.)