The generalized Ulam spiral displaying 81 numbers [La spirale d'Ulam généralisée montrant 81 nombres entiers].

Starting from the center of the picture, the 81 little squares are numbered (N=1, 2, 3,..., 81) when following a square spiral. The number 1 is the green square when the prime numbers are the white ones. The other squares are red with a luminance proportional to the number of divisors of N.

See some artistic variations:

[Plus d'informations à propos de la spirale d'Ulam et de ses généralisations -en français/in french-]
[More information about the Ulam spiral and ist generalizations -in english/en anglais-]

(CMAP28 WWW site: this page was created on 04/25/2012 and last updated on 08/22/2020 11:13:42 -CEST-)

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