196769domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumber of n-celled axially symmetric polyominoes without holes.at n=21A056879Numbers n such that n, 2n+1, 3n+2, 4n+3, 5n+4 are primes.at n=9A067258Primes that become squares when prefixed with an 8.at n=12A167741Prime numbersat n=17718