A216531 Numbers n such that (10^n + 1)/11 is prime and can be written in the form a^2 + 7*b^2.

7, 19, 31, 67, 2137, 268207

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