660

660 is the natural number that comes after 659 and before 661. It is an even, composite number with a prime factorization of 2^2 × 3 × 5 × 11. It has 24 positive divisors.

In various representations, 660 is written in Roman numerals as DCLX, and in binary it is 1010010100. It is a Harshad number in base 10, since the sum of its digits (6 + 6 + 0) equals 12 and 660 ÷ 12 = 55. The sum of all divisors of 660 is 2016, so the sum of its proper divisors is 1356. Because this exceeds 660, 660 is an abundant number, with an abundance of 696 (sigma(660) − 2×660).

Historically, traditional sources date the founding of Japan to 660 BCE, attributed to the legendary Emperor Jimmu. In modern infrastructure, the 660 area code covers much of northern Missouri in the United States, created in 1997 as a split from 816. In science and technology, 660 nanometers is a common wavelength for red light, widely used in LEDs and horticultural lighting.

Overall, 660 appears in arithmetic, numeral systems, historical chronology, telecommunications, and optical applications, reflecting its roles across mathematics and practical contexts.