A216549 Numbers n such that (10^n-1)/9 is prime, but cannot be written in the form a^2 + 3*b^2.

2, 23, 317, 1031, 86453

Offset

1,1

Comments

The exponent is congruent to 2 mod 3.

Links

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

Samuel S. Wagstaff, Jr., The Cunningham Project

Crossrefs

Subsequence of A004023.

Sequence in context: A088641 A077203 A173935 * A091693 A276025 A211925

Adjacent sequences: A216546 A216547 A216548 * A216550 A216551 A216552

Keyword

nonn

Author

V. Raman, Sep 08 2012

Status

approved