Business Number (BN)/ Registration Number – The BN is used by the federal government to identify organizations and the various program accounts they have. A complete BN has two parts: the registration number (first nine digits) and the account identifier (two letters and four digits). The registered charity account identifier always starts with the letters “RR”.

See http://www.cra-arc.gc.ca/chrts-gvng/dnrs/dctnry/menu-eng.html#bnnumber