The HICN issued by the RRB, may contain either 6 or 9 digit numbers with up to a 3-position letter prefix e.g., A123456 or MA123-45-6789. If a beneficiary's entitlement changes, it is possible for the 9-digit number, the prefix, the suffix or all three to change. It is also possible to go from an SSA issued HICN to a RRB HICN or vise versa. The numeric portion of a 9-digit HICN consists of a Social Security Number (SSN).