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..31.

Samuel S. Wagstaff, Jr. The Cunningham Project

Sequence in context: A130710 A145300 A240029 * A232637 A333383 A018322

Adjacent sequences: A216522 A216523 A216524 * A216526 A216527 A216528

nonn

V. Raman, Sep 08 2012

approved