911 (nine hundred
ndeleven) is the integer following 910 and preceding 912.
It is a
prime number
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
, a
Sophie Germain prime
In number theory, a prime number ''p'' is a if 2''p'' + 1 is also prime. The number 2''p'' + 1 associated with a Sophie Germain prime is called a . For example, 11 is a Sophie Germain prime and 2 × 11 + ...
and the sum of three consecutive primes (293 + 307 + 311). It is an
Eisenstein prime
In mathematics, an Eisenstein prime is an Eisenstein integer
: z = a + b\,\omega, \quad \text \quad \omega = e^,
that is irreducible (or equivalently prime) in the ring-theoretic sense: its only Eisenstein divisors are the units , itself ...
with no imaginary part and real part of the form 3''n'' − 1. Since 913 is a
semiprime
In mathematics, a semiprime is a natural number that is the product of exactly two prime numbers. The two primes in the product may equal each other, so the semiprimes include the squares of prime numbers.
Because there are infinitely many prime ...
, 911 is a
Chen prime
A prime number ''p'' is called a Chen prime if ''p'' + 2 is either a prime or a product of two primes (also called a semiprime). The even number 2''p'' + 2 therefore satisfies Chen's theorem.
The Chen primes are named after Chen Jingru ...
. It is also a
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. The centered decagonal number for ''n'' is given by th ...
.
There are 911
inverse semigroup In group (mathematics), group theory, an inverse semigroup (occasionally called an inversion semigroup) ''S'' is a semigroup in which every element ''x'' in ''S'' has a unique ''inverse'' ''y'' in ''S'' in the sense that ''x = xyx'' and ''y = yxy'', ...
s of order 7
911 is obtained by
concatenating
In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In certain formalisations of concatenati ...
its product of digits and sum of digits.
See also
*
9-1-1, a North American emergency telephone number
*
9/11, the September 11 attacks of 2001
*
AD 911
__NOTOC__
911 ( CMXI) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar.
Events
By place
Europe
* September 24 — King Louis IV (the Child), the last ruler of the Carolingian Dynasty ...
, a year
*
Porsche 911, a sports car
References
{{DEFAULTSORT:911 (Number)
Integers