863

863 is a prime number.

863 is the largest three-digit prime that can be written as the sum of fifteen consecutive primes: 29 + 31 + 37 + 41 + 43 + 47 + 53 + 59 + 61 + 67 + 71 + 73 + 79 + 83 + 89 = 863.

863 is a number that cannot be written as a sum of three squares.

863 = (11 + 71) + (11 x 71), where 11, 71, and 863 are all primes.

863 is a value of n so that n(n + 6) is a palindrome: 863(869) = 749947.

863 is a telephone area code for central Florida.

Source: Prime Curios!