1021

1021 is a natural number that follows 1020 and precedes 1022. In mathematics, it is a prime number. It is an emirp, since the reversal 1201 is also prime. In different bases, 1021 is written as 1111111101 in binary, 1775 in octal, and 0x3FD in hexadecimal.

1021 is used as a calendar year, notably in the early 11th century. During that year, the Byzantine Empire was ruled by Basil II; the Holy Roman Empire by Henry II; and the Song Dynasty by Emperor Zhenzong. Records from that year reflect ongoing political and military activity across Europe and East Asia, though details vary by region.