121 is the natural number following 120 and preceding 122. In mathematics, a natural number is either a positive integer (1, 2, 3, 4, ...) or a non-negative integer (0, 1, 2, 3, 4, ...). The former definition is generally used in number theory, while the latter is preferred in set theory. ... 120 (one hundred twenty in American English; one hundred and twenty in British English) is the natural number following 119 and preceding 121. ... 122 is the natural number following 121 and preceding 123. ...

In linguistics, cardinal numbers is the name given to number words that are used for quantity (one, two, three), as opposed to ordinal numbers, words that are used for order (first, second, third). ... Commonly, ordinal numbers, or ordinals for short, are numbers used to denote the position in an ordered sequence: first, second, third, fourth, etc. ... In mathematics, factorization or factoring is the decomposition of an object (for example, a number, a polynomial, or a matrix) into a product of other objects, or factors, which when multiplied together give the original. ... The system of Roman numerals is a numeral system originating in ancient Rome, and was adapted from Etruscan numerals. ... The binary numeral system (base-2) represents numeric values using two symbols, typically 0 and 1. ... In mathematics and computer science, hexadecimal, or simply hex, is a numeral system with a radix or base of 16 usually written using the symbols 0–9 and A–F or a–f. ...

In mathematics

One hundred twenty-one is a square and is the sum of three consecutive primes (37 + 41 + 43). There are no squares besides 121 known to be of the form 1 + p + p² + p³ + p⁴, where p is prime (3, in this case). There are only two other squares known to be of the form n! + 1. In algebra, the square of x is written x2 and is defined as the product of x with itself: x × x. ...

It is also a star number and a centered octagonal number. A star number, or centered 12-gonal number, is a centered figurate number that represents a centered hexagram, such as the one that Chinese checkers are played on. ... A centered octagonal number is a centered figurate number that represents an octagon with a dot in the center and all other dots surrounding the center dot in successive octagonal layers. ...

In base 10, it is a Smith number since its digits add up to the same value as its factorization (which uses the same digits) and as a consequence of that it is a Friedman number. But it can not be expressed as the sum of any other number plus that number's digits, making 121 a self number. A Smith number is a number which in a given base, the sum of its digits is equal to the sum of the digits in its factorization. ... A Friedman number is an integer which in a given base is the result of an expression using its own digits in combination with any of the four basic arithmetic operators (+, -, ×, ÷) and sometimes exponentiation. ... A self number or Colombian number is an integer which, in a given base, can not be generated by any other integer added to the sum of its digits. ...

In other fields

One hundred twenty-one is also:

• The number for voicemail for mobile phones on the Vodafone network
• The model number of the Lockheed EC-121, now on display at the Air Force Museum.
• The year AD 121 or 121 BC.
• The web-adress to the company one to one ab.