811

[Math.]  A prime number.

 

[Phone]  An NANPA/U.S. telephone area code reserves for special functions. This number cannot be used as area code.  (NANPA: North American Numbering Plan Administration).

 

[Phone]  A 7-digit number after an NANPA/U.S. 3-digit area code cannot start with 0nm, 1nm or 8 other 3-digit numbers: 211, 311, 411, 511, 611, 711, 811 and 911.

 

812...

 

813...

 

814...

 

815...

 

816...

 

817

 

818

[World]  The ISO-3166 country code for Egypt.

 

819

[Math.]  A pyramidal number (sum of all squares of integers from 1 to 13): 819 = 12+22+…+122+132.

 

[Math.]  Sum 273+546 = 819 is one of only 4 cases that the equality: n+2n = 3n use each of 9 digits 1-9 once: n = 192, 219, 273 and 327.

 

810-819

[Library]  Numbers 800-899 are the first 3 digits in Dewey Decimal Classification System call numbers for library books in Literature. Numbers 810-819 are for books in American Literature.