021

021 is a numeric string that can refer to different things depending on context. In ordinary decimal notation, 021 represents the number 21, with the leading zero not changing its value in decimal usage.

However, in some technical contexts the leading zero signals a different numeral system. In many programming languages, a leading zero denotes octal (base 8). The literal 021 therefore has the value 17 in decimal (2 times eight plus 1). Since not all languages consistently support octal literals, the meaning of 021 can vary; some languages disallow leading zeros or require a distinct prefix such as 0o to indicate octal.

In telecommunications and numbering plans, 021 can appear as part of a longer national number, often as an area code, trunk prefix, or domestic dialing indicator. The specific meaning and assignment are determined by the country’s numbering scheme, so interpretations of 021 are country-dependent.

In other uses, 021 may be employed as a model number, product code, file identifier, or other short label in catalogs, inventories, or datasets. As a compact identifier, its significance is entirely context-specific and typically defined by the system in which it appears.

See also: 21; octal numeral system; leading zeros.