811

811 is a prime number.

809 and 811 form a twin prime pair.

811 is the smallest prime that is a sum of primes beginning and ending with the digit 7: 811 = 7 + 7 + 797.

811 is the sum of five consecutive primes: 811 = 151 + 157 + 163 + 167 + 173.

811 is a prime of the form 4n + 3 that is the sum of two consecutive composite numbers: 811 = 4(202) + 3 = 405 + 406.

In the United States, the telephone number 811 has traditionally been a direct line to the business off of the telephone company providing service on the line.

Source: Prime Curios!