“…In order to avoid safety risks in communication and cryptography systems, it thus demands that the 4-adic complexity of a safe sequence s with period N should exceed N −16 6 , otherwise this sequence is so insecure that it can be decrypted by the RAA. In recent ten years, the research results of the 2-adic complexity of binary periodic sequences are rich [3,4,6,[15][16][17][18][19][20]25]. To the best of our knowledge, there are few literatures to study the 4-adic complexity of quaternary periodic sequences [2,13,14,21,22].…”