359860domain: NAppears in sequencesNumbers k such that 2*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=12A084832a(n) is the least positive integer in base n that when multiplied by 2n-1 will contain only the digits 0 and 1.at n=28A337624