911 (number)

911 (nine hundred [and] eleven) 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 semigroups of order 7 (sequence A001428 in OEIS)

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.

See also

• 911 C.E., the year
• 9-1-1, the telephone number of most local emergency agencies in the United States and Canada.