182521213001domain: NAppears in sequencesLargest prime factor of the "repunit" number 11...1 (cf. A002275).at n=23A003020Largest prime factor of 10^n - 1.at n=24A005422Greatest prime number p(n) with decimal fraction period of length n.at n=24A061075Prime factors of 10^100 - 1.at n=15A200861