Cartier's necklace number is not a pure number. The code of Cartier necklace consists of three parts: brand code, style code and size code. The brand code is 3 letters, representing Cartier; ; The style code is 4 digits, indicating the style of the necklace; The size code is a 2-digit number, indicating the size of the necklace. So the coding form of Cartier necklace is: CAR 12345678.