660 is both an ordinary integer and a year designation used in several calendars. As a calendar year, 660 (AD) is recorded as a leap year in the Julian system; as a number it sits between 659 and 661 and has a number of simple arithmetic properties that make it useful for classification and cataloging.

Arithmetic characteristics

As an integer, 660 is even and composite. Its prime factorization is 2^2 × 3 × 5 × 11. It has 24 positive divisors and a relatively large sum of divisors, making it an abundant number (the sum of its proper divisors exceeds the number itself).

  • Prime factorization: 2^2 × 3 × 5 × 11
  • Number of positive divisors: 24
  • Some divisors: 1, 2, 3, 4, 5, 6, 10, 11, 12, 15, 20, 22, 30, 33, 44, 55, 60, 66, 110, 132, 165, 220, 330, 660
  • Sum of all divisors (σ): 2016; sum of proper divisors: 1356 → classification: abundant
  • Roman numeral: DCLX

Year 660 (AD)

The year 660 in the Common Era falls in the seventh century, a period of considerable regional transformation. In East Asia, 660 is notable for developments on the Korean peninsula: the alliance between the Korean kingdom of Silla and the Tang dynasty of China led to the military defeat and collapse of the Baekje kingdom, an event that helped reshape political boundaries and influence in the region. In the broader Near Eastern and Mediterranean world the late 650s–early 660s form part of the era of rapid political change following the early Islamic expansions.

Year 660 (BCE) and traditional uses

The number 660 also appears as a year in ancient chronologies. In traditional Japanese chronology, 660 BCE is the legendary year given for the accession of Emperor Jimmu, the mythical founder of Japan according to later medieval chronicles; modern historians treat that date as part of national foundation myths rather than verified historical chronology.

Uses and notable facts

Beyond pure mathematics and calendrical usage, 660 appears frequently as an identifying number in modern contexts—model numbers, route designations, product codes and technical specifications. Because of its factor-rich structure, 660 is convenient in designing evenly divisible groupings or test cases in combinatorics and engineering examples.

In summary, 660 is a composite, abundant integer with a simple, memorable factorization. As a year it marks specific historical turning points in regional histories (notably in East Asia), and as a numeric label it continues to be used across many practical domains.