Ulam Spiral

primes on the integer lattice, and the diagonals nobody can explain

Plate VI
Integers0
Primes0
Density0%
Hover

Wind the integers outward in a square walk; the primes settle onto diagonal lines — values of n² + n + 41 and kin — for reasons still unproven. After S. Ulam · Los Alamos, 1963

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