501

501 is an integer that follows 500 and precedes 502. In mathematics it is a composite number with prime factorization 3 × 167, and its positive divisors are 1, 3, 167, and 501. In Roman numerals it is written as DI.

In various domains, 501 appears in several notable uses. Levi's 501 jeans are a classic button-fly denim style that was introduced in the 1890s and has remained a durable staple in casual fashion. The 501st Legion is a widely known international nonprofit fan organization dedicated to Star Wars costumes and charity work, active at public events and fundraising. HTTP status code 501, Not Implemented, is defined in web standards as a response indicating that the server does not support the functionality required to fulfill the request.

Legal and civic usages include section 501 of the United States Internal Revenue Code, which grants tax-exempt status to certain nonprofit organizations, most notably the 501(c)(3) category for charities, educational institutions, and similar groups, making donations to them tax-deductible in many cases. Area code 501 serves central Arkansas, including Little Rock, the state capital, within the North American Numbering Plan.

As a calendar designation, 501 can refer to the year AD 501 or 501 BCE in historical discussions.