234 primes!
Notes: 1. If p = 2, then: (a^2-1)/(a-1) = (a-1)(a+1)/(a-1) = (a+1) and that's allways prime if a=q-1 (where q is a prime number). 2. The only known numbers that are repunits with at least 3 digits in more than one base simultaneously are 31 (111 in base-5, 11111 in base-2) and 8191 (111 in base-90, 1111111111111 in base-2). The Goormaghtigh conjecture says there are only these two cases. 3. https://en.wikipedia.org/wiki/Repunit 4. https://oeis.org/A002384 5. Full title: Generalized Repunit Primes with 2^53 > b^p and p > 3 6. http://www.elektrosoft.it/matematica/repunit/repunit.htm
