In 1963, Stanislaw Ulam was bored at a lecture. He started writing numbers in a spiral and circling the primes. Diagonal lines appeared. Nobody fully knows why.
Grid size
300
Starting number
1
Color scheme
Pixel size
2
The diagonal lines correspond to certain quadratic polynomials that generate unusually many primes. Euler's famous n² + n + 41 is prime for n = 0 to 39 — and it traces a visible line in the spiral.