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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
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
Sequence in context: A326375 A358318 A071470 * A104461 A308042 A335694
KEYWORD
nonn
AUTHOR
Pierre CAMI, Oct 11 2011
STATUS
approved

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Last modified March 28 07:33 EDT 2024. Contains 371235 sequences. (Running on oeis4.)