A216533 Numbers n such that (10^n + 1)/11 is prime, but cannot be written in the form a^2 + 7*b^2.

5, 53, 293, 641, 3011

Offset: 1

Author

V. Raman, Sep 08 2012

Keywords

• nonn

Comments

These exponents are congruent to {2, 4, 5} mod 6.

Links

• Samuel S. Wagstaff, Jr. The Cunningham Project

Crossrefs

Cf. A001562.