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 units 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. It is the first 4-digit integer.
Notation
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 or 210).
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 "$30k" for $30,000 or using "Y2K" to denote the Year 2000 computer problem.
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.
In mathematics
A chiliagon is a 1000-sided polygon.
Numbers in the range 1001–1999
1001 to 1099
1001 = sphenic number (7 × 11 × 13), pentagonal number, pentatope number, palindromic number
1002 = sphenic number, Mertens function zero, abundant number, number of partitions of 22
1003 = the product of some prime p and the pth prime, namely p = 17.
1004 = heptanacci number
1005 = Mertens function zero, decagonal pyramidal number
1006 = semiprime, product of two distinct isolated primes (2 and 503); unusual number; square-free number; number of compositions (ordered partitions) of 22 into squares; sum of two distinct pentatope numbers (5 and 1001); number of undirected Hamiltonian paths in 4 by 5 square grid graph; record gap between twin primes; number that is the sum of 7 positive 5th powers. In decimal: equidigital number; when turned around, the number looks like a prime, 9001; its cube can be concatenated from other cubes, 1_0_1_8_1_0_8_216 ("_" indicates concatenation, 0 = 03, 1 = 13, 8 = 23, 216 = 63)
1007 = number that is the sum of 8 positive 5th powers
1008 = divisible by the number of primes below it
1009 = smallest four-digit prime, palindromic in bases 11, 15, 19, 24 and 28: (83811, 47415, 2F219, 1I124, 18128). It is also a Lucky prime and Chen prime.
1010 = 103 + 10, Mertens function zero
1011 = the largest n such that 2n contains 101 and does not contain 11011, Harshad number in bases 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 (and 202 other bases), number of partitions of 1 into reciprocals of positive integers <= 16 Egyptian fraction
1012 = ternary number, (3210) quadruple triangular number (triangular number is 253), number of partitions of 1 into reciprocals of positive integers <= 17 Egyptian fraction
1013 = Sophie Germain prime, centered square number, Mertens function zero
1014 = 210-10, Mertens function zero, sum of the nontriangular numbers between successive triangular numbers 78 and 91
1015 = square pyramidal number
1016 = member of the Mian–Chowla sequence, stella octangula number, number of surface points on a cube with edge-length 14
1017 = generalized triacontagonal number
1018 = Mertens function zero, 101816 + 1 is prime
1019 = Sophie Germain prime, safe prime, Chen prime
1020 = polydivisible number
1021 = twin prime with 1019. It is also a Lucky prime.
1022 = Friedman number
1023 = sum of five consecutive primes (193 + 197 + 199 + 211 + 223); the number of three-dimensional polycubes with 7 cells; number of elements in a 9-simplex; highest number one can count to on one's fingers using binary; magic number used in Global Positioning System signals.
1024 = 322 = 45 = 210, 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). 1024 is the smallest 4-digit square and also a Friedman number.
1025 = Proth number 210 + 1; member of Moser–de Bruijn sequence, because its base-4 representation (1000014) contains only digits 0 and 1, or it's a sum of distinct powers of 4 (45 + 40); Jacobsthal-Lucas number; hypotenuse of primitive Pythagorean triangle
1026 = sum of two distinct powers of 2 (1024 + 2)
1027 = sum of the squares of the first eight primes; can be written from base 2 to base 18 using only the digits 0 to 9.
1028 = sum of totient function for first 58 integers; can be written from base 2 to base 18 using only the digits 0 to 9; number of primes <= 213.
1029 = can be written from base 2 to base 18 using only the digits 0 to 9.
1030 = generalized heptagonal number
1031 = exponent and number of ones for the fifth base-10 repunit prime, Sophie Germain prime, super-prime, Chen prime
1032 = sum of two distinct powers of 2 (1024 + 8)
1033 = emirp, twin prime with 1031
1034 = sum of 12 positive 9th powers
1035 = 45th triangular number, hexagonal number
1036 = central polygonal number
1037 = number in E-toothpick sequence
1038 = even integer that is an unordered sum of two primes in exactly 40 ways
1039 = prime of the form 8n+7, number of partitions of 30 that do not contain 1 as a part, Chen prime, Lucky prime
1040 = 45 + 42: sum of distinct powers of 4. The number of pieces that could be seen in a 6 × 6 × 6× 6 Rubik's Tesseract.
1041 = sum of 11 positive 5th powers
1042 = sum of 12 positive 5th powers
1043 = number whose sum of even digits and sum of odd digits are even
1044 = sum of distinct powers of 4