These are the prime numbers in A121153. Some of these primes are in A076481, the base-3 repunit primes, which have the form (3^n-1)/2. However, 757 has base-3 representation 1001001 and a base-27 representation 111. Are more exceptions?
Contains A076481 as a subsequence, implying that a(6) <= A076481(4) = 3754733257489862401973357979128773. - Max Alekseyev, Aug 17 2013