209

209 is a natural number that follows 208 and precedes 210. It is used in various contexts including mathematics, science, and geography.

In mathematics, 209 is a composite number. Its prime factorization is 11 × 19, making it a semiprime. In different numeral systems, 209 is written as 11010001 in binary, 321 in octal, and D1 in hexadecimal. In Roman numerals, it is CCIX.

In science, 209 is associated with the isotope Bismuth-209 (Bi-209). Bi-209 is the heaviest stable isotope of bismuth; it is characterized by an extremely long half-life, with decay so rare that it has not been observed within the age of the universe, estimated on the order of 10^19 years.

In telecommunications, 209 is the area code assigned to a large portion of California’s Central Valley, covering cities and counties such as Stockton, Modesto, and surrounding communities. Area code 209 is used for wire line and mobile telephone services within that region.

As a year, 209 can refer to events dated to either 209 CE in the Common Era or 209 BCE in the pre-Common Era, placing it within ancient Roman and other historical timelines.