Concept
1000 or one thousand is the natural number following 999 and preceding 1001. In most English-speaking countries, it can be written with or without a comma or sometimes a period separating the thousands digit: 1,000. A group of one thousand things is sometimes known, from Ancient Greek, as a chiliad. A period of one thousand years may be known as a chiliad or, more often from Latin, as a millennium. The number 1000 is also sometimes described as a short thousand in medieval contexts where it is necessary to distinguish the Germanic concept of 1200 as a long thousand. The decimal representation for one thousand is 1000—a one followed by three zeros, in the general notation; 1 × 103—in engineering notation, which for this number coincides with: 1 × 103 exactly—in scientific normalized exponential notation; 1 E+3 exactly—in scientific E notation. The SI prefix for a thousand units is "kilo-", abbreviated to "k"—for instance, a kilogram or "kg" is a thousand grams. This is sometimes extended to non-SI contexts, such as "ka" (kiloannum) being used as a shorthand for periods of 1000 years. In computer science, however, "kilo-" is used more loosely to mean 2 to the 10th power (1024). In the SI writing style, a non-breaking space can be used as a thousands separator, i.e., to separate the digits of a number at every power of 1000. Multiples of thousands are occasionally represented by replacing their last three zeros with the letter "K" or "k": for instance, writing "30 000 or denoting the Y2K computer bug of the year 2000. A thousand units of currency, especially dollars or pounds, are colloquially called a grand. In the United States, this is sometimes abbreviated with a "G" suffix. There are 168 prime numbers less than 1000. 1000 is the 10th icositetragonal number, or 24-gonal number. 1000 has a reduced totient value of 100, and totient of 400. It is equal to the sum of Euler's totient function over the first 57 integers, with 11 integers having a totient value of 1000.