031

031 is a three‑digit numeral that may appear in various contexts, including mathematics, telecommunications, transportation, and cultural references. In base‑10 notation the value of 031 is equal to 31; the leading zero is often used to maintain a fixed‑width format in catalogues, serial numbers or computer strings.

In mathematics, 31 is a prime number, the eleventh prime, and it is a Mersenne prime exponent because 2^31 − 1 yields a large Mersenne prime. The binary representation of 31 is 11111, which is the smallest five‑bit repunit. In decimal, 31 is also a centered triangular number and appears in several combinatorial identities.

Telecommunication systems frequently employ three‑digit codes that begin with a leading zero. The prefix 031 is assigned as a national dialing code in several countries. In Belgium, 031 serves the area surrounding the city of Leuven and its environs. In the Netherlands, the area code 031 designates parts of Limburg, including the city of Venlo. Other uses include internal extensions for corporate phone systems and vehicle registration prefixes in certain jurisdictions.

Transportation networks sometimes use 031 to label routes or services. For example, some regional bus lines or railway services in Europe and Asia are numbered 031 to differentiate them from other lines. In the aviation industry, aircraft tail numbers or flight numbers may incorporate 031 as part of a sequential series.

The string “031” also appears in product model numbers, software versioning, and as an identifier in databases where fixed‑length fields are required. Its prevalence across disparate fields illustrates the practical role of leading zeros in maintaining uniform data formats.