551

551 is the natural number that follows 550 and precedes 552. It is an odd, composite number. Its prime factorization is 19 × 29, so 551 is a semiprime. The divisors are 1, 19, 29, and 551.

In different numeral systems, 551 is represented as 0b1000100111 in binary and as 0x227 in hexadecimal. In Roman numerals it is written as DLI.

As a year, 551 CE falls in the 6th century and occurred during the era of the Byzantine Empire, under Justinian I. The year sits in a period of ongoing classical-to-early-medieval transitions in the Mediterranean region.

In astronomy, 551 Ortrud is a minor planet in the asteroid belt, discovered in 1904 by August Kopff and named Ortrud.

In popular culture, 551 Horai is the name of a well-known chain of Chinese-style steamed buns restaurants in Japan, famous for nikuman.