911 (number)

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For other uses of "911", see 911 (disambiguation).

911 (nine hundred [and] eleven) is the number following 910 and preceding 912.

911
List of numbers — Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	Nine hundred [and] eleven
Ordinal	911th
Factorization	Prime
Roman numeral	CMXI
Binary	1110001111
Hexadecimal	38F

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 $3 n - 1$ . Since 913 is a semiprime, 911 is a Chen prime. It is also a centered decagonal number.

911 (nine-one-one) is the telephone number of most local emergency agencies (such as the police or the fire department) in the United States and Canada.

As "911" or "9/11", typically pronounced "nine-eleven", it is commonly used to refer the calendar dates 9 November 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.

There were 912 days between the September 11, 2001 attacks and the March 11 2004 Madrid train bombings, which is a very close number to 911, but counterterrorism experts disagree if that's why the date was chosen.^[1]