The angle between A and B is a right-angle, 90°.
(3,4,5)(3,4,5) is the best known Pythagorean Triple: integers that satisfy the equation
This equation is familiar from Pythagoras' Theorem: in a right angle triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides. As a result your vectors A, B, C form a right-angled triangle.
Other well-known Pythagorean Triples are:
and there are 16 such primitive triples with hypotenuse less than 100. There are also non-primitive triples such as (6,8,10)(6,8,10) that are multiples of the primitive triples.