Year 421 (CDXXI) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Agricola and Eustathius (or, less frequently, year 1174 Ab urbe condita). The denomination 421 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

This page details the format and usage of telephone numbers in Slovakia. Today, Slovakia uses a closed numbering plan with area codes beginning with 0. After 0, there is usually a 2-digit prefix, followed by a 7-digit subscriber number. The capital, Bratislava, has one-digit prefix and an 8-digit subscriber number.