174469domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumber of n X n binary arrays symmetric about main diagonal with all ones connected only in a 1100-1111-1100 pattern in any orientation.at n=13A147477Primes p such that p-2, p^2-2 and p^3-2 are all prime.at n=20A270972Prime numbersat n=15874