## Reblog: Animated Sieve of Eratosthenes

The Math Less Traveledhas a lovely video here, animating the Sieve of Eratosthenes, one of the classic methods of finding all of the prime numbers one wants. I suppose it won’t eliminate writing out and crossing off numbers for extra credit on a math test. I actually remember that being one test I had in, I believe, seventh grade, for reasons that I don’t think I ever got. Possibly the teacher wanted to have an easy time grading, or was giving everyone a break from too much computation by shifting to evaluation of our crossing-out abilities.

Here’s something I made yesterday! (Note, I strongly suggest watching it fullscreen, in HD if you have the bandwidth for it.)

Can you figure out what’s going on? The source code for the animation is here; I was inspired by Jason Davies’ visualization which was in turn inspired by this.

## educationrealist 4:31 am

onFriday, 12 April, 2013 Permalink |That’s gorgeous.

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## Joseph Nebus 2:17 pm

onFriday, 12 April, 2013 Permalink |It is. I’m surprised how lovely something simple like this can be, given the chance.

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## natalie 3:00 pm

onSunday, 14 April, 2013 Permalink |what does each moving curve represent?

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## Joseph Nebus 5:17 am

onTuesday, 16 April, 2013 Permalink |I’m sorry to be slow answering; I was occupied all weekend.

The (semi-)circles have diameters of 2, 3, 5, 7, 11, and so on. Each one intersects the center line at multiples of their respective diameter. The numbers on the center line that don’t get a semicircle intersecting it after all the smaller loops have gotten past it are the prime numbers sifted out.

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