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A197118
Number of k such that (2^k+1)*2^n-1 is prime with 0 < k < n+1.
4
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
OFFSET
1,2
COMMENTS
As n increases sum a(n) from 1 to n / n tends to 2.66.
PROG
(PARI) a(n) = sum(k=1, n, isprime((2^k+1)*2^n-1)); \\ Michel Marcus, Sep 21 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Oct 11 2011
STATUS
approved