ICOT,
3,4, and 5 are a pythagorean triple. That is, they can form the sides of a right triangle, where 5 is the side opposite the right angle. Then, according to the Pythagorean Theorem, 3^2 + 4^2 = 5^2 (9+16=25). Another example of a unique Pythagorean Triple would be 5,12, and 13.