818

This number is a composite.

818 is the smallest palindrome that may be expressed as the sum of the squares of two primes (23² + 17²). [King]

818 is the only 3-digit tetradic integer such that the sum of the differences of the number and each digit raised to the digit is prime. I.e., (818-8)^8+(818-1)^1+(818-8)^8 is prime. [Opao]