259829domain: NPropertiesPrimalityPrimeyesAppears in sequencesa(n) = 9*b_9(n) + 8, where b_9 lists the indices of zeros of the sequence A261309: u(n) = abs(u(n-1) - gcd(u(n-1), 9n-1)), u(1) = 1.at n=4A186261Prime numbersat n=22826