The generalized Ulam spiral (La spirale d'Ulam généralisée)

From AVirtualSpaceTimeTravelMachine: "Starting from the center of the picture, the points are numbered (1, 2, 3,...) when following a square spiral. The radius of the N-th sphere is proportional to the number of divisors of N."

[via Rafa Villota and Cliff Pickover who wrote, "Wondrous visualization of mysterious patterns in prime numbers."]

Concur.