A charity registration number is 15-digit program account number assigned to a charity by the CRA when it is registered. A complete charity registration number has three parts: the BN (first nine digits), the program identifier (two letters), and the reference number (four digits). The registered charity program identifier is "RR". When you deal with the Charities Directorate always use the 15-digit registration number.
(CRA : Charities Glossary)