190787domain: NPropertiesPrimalityPrimeyesAppears in sequencesPrimes that remain prime through 3 iterations of function f(x) = 8x + 1.at n=21A023291Number of 321-hexagon-avoiding permutations in S_n, i.e., permutations of 1..n with no submatrix equivalent to 321, 56781234, 46781235, 56718234 or 46718235.at n=12A058094Prime numbersat n=17229