5794777domain: NPropertiesPrimalityPrimeyesAppears in sequencesIndices of prime repunits: numbers k such that 11...111 (with k 1's) = (10^k - 1)/9 is prime.at n=9A004023Numbers k such that 11...111 (with k 1's) = (10^k - 1)/9 is a Kaprekar prime.at n=3A350755Prime numbersat n=399663