# Experimenting with the Ulam Spiral

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The Ulam spiral is named after Stanislaw Ulam, who discovered it by chance in 1963 while doodling on scratch paper at a scientific meeting.

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Integers are placed on a square spiral. By marking the prime numbers, you can see that they tend to form patterns lining up in diagonal, horizontal, and vertical lines. This phenomenon can be best observed by drawing a large number of primes.

When starting the spiral with 41, a long diagonal line is clearly visible.

Triangular numbers (of the form ) as well as pentagonal numbers (of the form ) give rise to pinwheel patterns on the spiral.

Some things to try

• Play "number of integers" and/or "start from" to see how spiral patterns evolve.

• Set "number of integers" to its maximum and observe the pattern, a very regular, pleasant, spiral shape.

• Slide "start from" to its maximum. Notice the pattern disappears. It looks just like random noise.

• Play "number of integers" and/or "start from" to watch spiral patterns evolve.

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Contributed by: Giovanna Roda (March 2011)
Open content licensed under CC BY-NC-SA

## Details

Triangle Numbers on Ulam Spiral by Adrian Leatherland http://yoyo.cc.monash.edu.au/~bunyip/primes/triangleUlam.htm

Ulam Spiral Images by Matthew M. Conroy at http://www.madandmoonly.com/doctormatt/mathematics/ulamSpirals/ulamSpirals.htm

Ulam spiral at http://en.wikipedia.org/wiki/Ulam_spiral

## Permanent Citation

Giovanna Roda

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