478243domain: NPropertiesPrimalityPrimeyesAppears in sequencesPrime factors of numbers in A006521 (numbers k that divide 2^k + 1).at n=21A057719Prime divisors of solutions to 10^n == 1 (mod n).at n=23A066364Larger member of twin prime pairs whose sum is a square.at n=24A118593Prime numbersat n=39868