820

820 is a natural number that comes after 819 and before 821. It is an even composite number. The prime factorization is 2^2 × 5 × 41. Its positive divisors are 1, 2, 4, 5, 10, 20, 41, 82, 164, 205, 410, and 820. The sum of all divisors is 1,764, and the sum of its proper divisors is 944. Because 944 exceeds 820, 820 is an abundant number. In Roman numerals, 820 is written as DCCCXX.

In decimal form it is 820. In other common bases, it is 0x334 in hexadecimal, 0o1464 in octal, and 1100110100 in binary.

Historically, the year 820 CE falls in the early medieval period. It lies within the era of the Carolingian Empire, during the reign of Louis the Pious, and is associated with the era’s dynastic and political dynamics that would eventually lead to the division of the realm in the following century. The 9th century was marked by increasing Viking activity in Western Europe, and events around 820 are often considered within that broader context of early medieval history.

See also: related numbers and calendar context.