911 (number)
Encyclopedia
911 is the number following 910 and preceding 912.
It is a prime number
, a Sophie Germain prime
and the sum of three consecutive primes (293 + 307 + 311). It is an Eisenstein prime
with no imaginary part and real part of the form 3n − 1. Since 913 is a semiprime
, 911 is a Chen prime
. It is also a centered decagonal number
.
There are 911 inverse semigroup
s of order 7
911 is obtained by concatenating its sum of digits and product of digits.
The Madrid Attack came exactly 911 days after 9/11
.
As "911" or "9/11", typically pronounced "nine-eleven", it is commonly used to refer the calendar dates November 9 or September 11, depending on which date notation
is used. The latter usage most commonly refers to the September 11, 2001 attacks
in the United States.
| 911 | |
|---|---|
| Cardinal Cardinal number In mathematics, cardinal numbers, or cardinals for short, are a generalization of the natural numbers used to measure the cardinality of sets. The cardinality of a finite set is a natural number – the number of elements in the set. The transfinite cardinal numbers describe the sizes of infinite... |
Nine hundred and eleven |
| Ordinal Ordinal number In set theory, an ordinal number, or just ordinal, is the order type of a well-ordered set. They are usually identified with hereditarily transitive sets. Ordinals are an extension of the natural numbers different from integers and from cardinals... |
911th |
| Factorization Factorization In mathematics, factorization or factoring is the decomposition of an object into a product of other objects, or factors, which when multiplied together give the original... |
Prime |
| Roman numeral | CMXI |
| Binary Binary numeral system The binary numeral system, or base-2 number system, represents numeric values using two symbols, 0 and 1. More specifically, the usual base-2 system is a positional notation with a radix of 2... |
1110001111 |
| Hexadecimal Hexadecimal In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen... |
38F |
It is a prime number
Prime number
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example 5 is prime, as only 1 and 5 divide it, whereas 6 is composite, since it has the divisors 2...
, a Sophie Germain prime
Sophie Germain prime
In number theory, a prime number p is a Sophie Germain prime if 2p + 1 is also prime. For example, 23 is a Sophie Germain prime because it is a prime and 2 × 23 + 1 = 47, and 47 is also a prime number...
and the sum of three consecutive primes (293 + 307 + 311). It is an Eisenstein prime
Eisenstein prime
In mathematics, an Eisenstein prime is an Eisenstein integerz = a + b\,\omega\qquadthat is irreducible in the ring-theoretic sense: its only Eisenstein divisors are the units , a + bω itself and its associates.The associates and the complex conjugate...
with no imaginary part and real part of the form 3n − 1. Since 913 is a semiprime
Semiprime
In mathematics, a semiprime is a natural number that is the product of two prime numbers. The first few semiprimes are 4, 6, 9, 10, 14, 15, 21, 22, 25, 26, ... ....
, 911 is a Chen prime
Chen prime
A prime number p is called a Chen prime if p + 2 is either a prime or a product of two primes. The even number 2p + 2 therefore satisfies Chen's theorem....
. It is also a centered decagonal number
Centered decagonal number
A centered decagonal number is a centered figurate number that represents a decagon with a dot in the center and all other dots surrounding the center dot in successive decagonal layers...
.
There are 911 inverse semigroup
Inverse semigroup
In mathematics, an inverse semigroup S is a semigroup in which every element x in S has a unique inversey in S in the sense that x = xyx and y = yxy...
s of order 7
911 is obtained by concatenating its sum of digits and product of digits.
The Madrid Attack came exactly 911 days after 9/11
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...
.
As "911" or "9/11", typically pronounced "nine-eleven", it is commonly used to refer the calendar dates November 9 or September 11, depending on which date notation
Date and time notation
Date and time notation around the world varies.An approach to harmonise the different notations is the ISO 8601. Since the Internet is a main enabler of communication between people with different date notation background, and software is used to facilitate the communication, RFC standards and W3C...
is used. The latter usage most commonly refers to the September 11, 2001 attacks
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...
in the United States.
See also
- 911911Year 911 was a common year starting on Tuesday of the Julian calendar.-Africa:* Rebellion of the Kutama Berbers against the Fatimid Caliphate...
C.E., the year - 9-1-19-1-19-1-1 is the emergency telephone number for the North American Numbering Plan .It is one of eight N11 codes.The use of this number is for emergency circumstances only, and to use it for any other purpose can be a crime.-History:In the earliest days of telephone technology, prior to the...
, the telephone numberTelephone numberA telephone number or phone number is a sequence of digits used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator...
of most local emergency agencies in the United States and Canada.