- published: 08 Sep 2011
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1000 or 1,000 (one thousand) is the natural number following 999 and preceding 1001.
, the number of bytes in a kilobyte (in 1999, the IEC coined kibibyte to use for 1024 with kilobyte being 1000, but this convention has not been widely adopted)
, nonagonal number, centered octagonal number
, octahedral number, centered pentagonal number
, triangular number, square triangular number, hexagonal number, centered octagonal number
, Failed to parse (Missing texvc executable; please see math/README to configure.): 7^2 + 8^2 + \cdots + 16^2 , centered square number
, smallest pandigital number in Roman numerals
, Mertens function zero, centered octagonal number, forms a Ruth–Aaron pair with 1520 under second definition
, street number on Pennsylvania Avenue of the White House, Meters; Common High School Track Event, perfect score on SAT
, smallest number yielded by the formula Failed to parse (Missing texvc executable; please see math/README to configure.): n^2 + n + 41
, centered octagonal number
1991 (MCMXCI) was a common year starting on Tuesday (link will display full calendar) of the Gregorian calendar in the 20th century. It was the second year of the 1990s, and is usually considered the final year of the Cold War that had begun in the late 1940s. During the year, the Union of Soviet Socialist Republics collapsed into fifteen sovereign republics. A U.N.-authorized coalition force from thirty-four nations fought against Iraq, which had invaded Kuwait in the previous year, 1990. The conflict would be called the Gulf War. The year 1991 was the 1991st year of Anno Domini, the 991st year of the 2nd millennium, the 91st year of the 20th century and 2nd in the 1990s.
A number is a mathematical object used to count and measure. In mathematics, the definition of number has been extended over the years to include such numbers as zero, negative numbers, rational numbers, irrational numbers, and complex numbers.
Mathematical operations are certain procedures that take one or more numbers as input and produce a number as output. Unary operations take a single input number and produce a single output number. For example, the successor operation adds one to an integer, thus the successor of 4 is 5. Binary operations take two input numbers and produce a single output number. Examples of binary operations include addition, subtraction, multiplication, division, and exponentiation. The study of numerical operations is called arithmetic.
A notational symbol that represents a number is called a numeral. In addition to their use in counting and measuring, numerals are often used for labels (telephone numbers), for ordering (serial numbers), and for codes (e.g., ISBNs).