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A216531 Numbers n such that (10^n + 1)/11 is prime and can be written in the form a^2 + 7*b^2. 0
7, 19, 31, 67, 2137, 268207 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These exponents are congruent to {0, 1, 3} mod 6.

LINKS

Table of n, a(n) for n=1..6.

Samuel S. Wagstaff, Jr. The Cunningham Project

CROSSREFS

Cf. A001562.

Sequence in context: A234310 A141338 A237366 * A216564 A145042 A153892

Adjacent sequences:  A216528 A216529 A216530 * A216532 A216533 A216534

KEYWORD

nonn

AUTHOR

V. Raman, Sep 08 2012

STATUS

approved

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Last modified November 20 13:05 EST 2018. Contains 317402 sequences. (Running on oeis4.)