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

Author

V. Raman, Sep 08 2012

Keywords

• nonn

Comments

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

Links

• Samuel S. Wagstaff, Jr. The Cunningham Project

Crossrefs

Cf. A001562.