If 1, 2, 3, ... are simply placed in a line, primes appear scattered without any pattern. But arrange the numbers in a spiral and primes often appear along diagonal lines. Mathematician Stanisław Ulam reportedly discovered this while doodling during a boring meeting in 1956.
Place 1 at the center, then fill 2, 3, 4, ... in a growing spiral, moving right → up → left → down.
Mark primes (numbers divisible only by 1 and themselves) as dots and leave the rest blank. The primes then appear unusually often along certain diagonals — a pattern that mathematicians still cannot fully explain.