A Medicare number is comprised of the taxpayer's Social Security number followed by a code that identifies the type of recipient, according to OCMedicare.com. For example, A refers to the primary claimant, and B indicates a wife of a primary claimant who is age 62 or over, according to Q1Medicare.com.
The code may consist of one letter or a letter and a number. B1 indicates a husband of the primary claimant who is age 62 or older, while B6 refers to a divorced wife age 62 or older. C codes relate to children, and D, E and W codes identify widows and widowers. The F series refers to aged dependent parents, according to Q1Medicare.com.