What is the Ulam Spiral?
The Ulam Spiral starts with any number in the middle. And then draws the next numbers spiralizing around this start number. If a number in the Spiral is a prime number it gets a marking. Although the prime numbers seem to be random, you will see a signifikant clustering of prime numbers in diagonals.
For detailed Information and the history of the Ulam Spiral see Wikipedia. The iphone App shows three kinds of ulam spirals: Square Spirals (in the date section) , Sacks-Spirals (in the nuber section) and Fibonacci Spirals(in the time section). Zoom in to see the leading spiral lines. Take a long tap to get more Information about the selected Number.
There is an open Question: Is the ulam spiral of a number unique? No surely not, but can a finite part of the ulam spiral uniquely identify the starting number? Related infos on youtube: Last Digit of Prime Numbers
