576

This number is a composite.

576 = sigma(5*7*6). Note that 576 is the first multi-digit number with this property. [Firoozbakht]

A square equal to (2 + 3 + 5 + 7 + 11)² - (2² + 3² + 5² + 7² + 11²). It's the only such case for all primes < 2,000,000,000. [Trotter and De Geest]

576 is the largest known square that divides the concatenation of its prime factors, where the order of its prime factors can be arranged freely, i.e. 576 = 2 * 2 * 2 * 2 * 3 * 2 * 3 * 2, and 576 divides 22223232. [Rivera]