Papers purporting to be an international application under Rule 20.1(a) shall be allocated an international application number, consisting of the letters "PCT," a slant, the two-letter code referred to in Section 115, indicating the receiving Office, a four-digit indication of the year in which such papers were first received, a slant and a six-digit number, allotted in sequential order corresponding to the order in which the international applications are received (e.g., "PCT/SE2004/000001"). Where the International Bureau acts as receiving Office, the two-letter code "IB" shall be used.