Ulam Spiral
The Ulam Spiral is a method of visualizing the prime numbers discovered by chance by the mathematician Stanislaw Ulam in 1963.
The spiral is constructed on a regular rectangular grid of numbers, starting with 1 at the center, and spiraling out. As shown above, prime numbers are very often aligned on diagonals, which is unexpected and unexplained but leads to the development of new methods for generating or testing prime numbers. Visualization was required to discover this phenomena that scales to very large sizes.