1872113domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumber of n X n symmetric binary matrices with each 1 adjacent to no more than 1 horizontally or vertically neighboring 1.at n=6A191506Primes p such that 2p-1 is a square and 2p+1 is also prime.at n=27A386995Prime numbersat n=140101