Nominal numbers are numbers used for identification only. They do not indicate quantity, rank, or any other measurement. However they may encode information.
The properties of nominal numbers are the minimum required to refer to an entity as a number.
Examples of nominal numbers include; sport jersey numbers; telephone numbers; zip codes; transportation route numbers; etc.
Operations with nominal numbers
A Nominal number is a numeral, or a string of numerals that is used for identification only, so that the only valid operation that may be carried out with nominal numbers is comparison. That is, two or more nominal numbers can be compared to determine if they are identical; while this may seem trite, it is a distinction important for computer science.
The converse of this is that any other mathematical operation done with or upon nominal numbers yields nonsense. The pseudo-science of numerology rejects this, instead declaring the opposite as a fundamental tenet.
See also