47237domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumbers n such that 6*10^n + 3*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=21A103033Primes p such that there exist primes p'<p"<p"'<p""<p such that the concatenation of any two among the {p,...,p""} is prime.at n=7A139005Prime numbersat n=4871