225

This number is a composite.

The number 225^n + 2 is prime for half of the numbers from one to ten. [Patterson]

The smallest square that can be can be written as the sum of a cube and a square (a^3 + b^2) in two ways, i.e., 225=5^3+10^2=6^3+3^2. [Loungrides]

The smallest prime-digit square that is arithmetic mean of two consecutive primes (223+227)/2. [Bajpai]