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

1,1

Comments

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

Links

Table of n, a(n) for n=1..5.

Samuel S. Wagstaff, Jr. The Cunningham Project

Crossrefs

Cf. A001562.

Sequence in context: A058867 A058869 A054342 * A152473 A242906 A068170

Adjacent sequences: A216530 A216531 A216532 * A216534 A216535 A216536

Keyword

nonn

Author

V. Raman, Sep 08 2012

Status

approved