1,2

These repunit numbers of the form (10^n-1)/9 have no prime factors congruent to 3 (mod 7) or 5 (mod 7) or 6 (mod 7) to an odd power. Also the power of 2 is not 1.

Table of n, a(n) for n=1..27.

Samuel S. Wagstaff, Jr. The Cunningham Project

Sequence in context: A058620 A038910 A035497 * A059335 A070419 A080199

Adjacent sequences: A216524 A216525 A216526 * A216528 A216529 A216530

nonn

V. Raman, Sep 08 2012

approved