If you start with the number 1, and then start plotting sequential integers (1, 2, 3) in a square spiral -- like so:
prime numbers have a curious tendency to cluster along diagonal lines rotated 45 degrees from the orientation of the spiral.
This loose pattern is called Ulam's Spiral.
When I look at the above image and unfocus my eyes, my brain bifurcates the spiral into 4 quadrants. I suspect this is due to continuous use of Cartesian Coordinate graphs throughout my education.
Word of the day: Apophenia
The tendency to perceive meaning in patterns formed within random, unrelated data.