911 (number)
911 is the integer following 910 and preceding 912.
It is a prime number, a Sophie Germain prime and the sum of three consecutive primes. 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 semigroups of order 7
911 is obtained by concatenating its product of digits and sum of digits.
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 North American emergency telephone number, see 9-1-1, or the September 11, 2001 attacks in the United States.
