18953251domain: NPropertiesPrimalityPrimeyesAppears in sequencesa(n) = 4*b_4(n)+3, where b_4 lists the indices of zeros of the sequence A261304: u(n) = abs(u(n-1)-gcd(u(n-1),4*n-1)), u(1) = 1.at n=9A186256Prime numbersat n=1208269