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A216519 Prime numbers n such that 2^n-1 is a prime that cannot be written in the form a^2+7*b^2. 1
2, 5, 17, 89, 107, 521, 4253, 9689, 9941, 11213, 19937, 21701, 86243, 756839, 859433, 1398269, 2976221, 3021377, 6972593, 25964951, 32582657, 37156667, 43112609 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The terms are congruent to 2 (mod 3).

LINKS

Table of n, a(n) for n=1..23.

Samuel S. Wagstaff, Jr. The Cunningham Project

CROSSREFS

Cf. A216518.

Sequence in context: A162042 A162043 A016121 * A245108 A195137 A026822

Adjacent sequences:  A216516 A216517 A216518 * A216520 A216521 A216522

KEYWORD

nonn

AUTHOR

V. Raman, Sep 08 2012

STATUS

approved

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Last modified April 4 19:22 EDT 2020. Contains 333229 sequences. (Running on oeis4.)