One of the pleasures of exploring an ancient city like York or Chester is that of learning new routes to the same destination. There are byways and alleys, short-cuts and diversions. You set off intending to go to one place and end up in another.

Maths is like that, even at its simplest. There are many routes to the same destination. I first found the fractal below by playing with the L-triomino, or the shape created by putting three squares in the shape of an L. You can divide it into four copies of the same shape and discard one copy, then do the same to each of the sub-copies, then repeat. I’ve decided to call it the hourglass fractal:

Hourglass fractal (animated)

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Hourglass fractal (static)

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Then I unexpectedly came across the fractal again when playing with what I call a proximity fractal:

Hourglass animated (proximity fractal)

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(Static image)

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Now I’ve unexpectedly come across it for a third time, playing with a very simple fractal based on a 2×2 square. At first glance, the 2×2 square yields only one interesting fractal. If you divide the square into four smaller squares and discard one square, then do the same to each of the three sub-copies, then repeat, you get a form of the Sierpiński triangle, like this:

Sierpiński triangle stage 1

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Sierpiński triangle #2

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Sierpiński triangle #3

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Sierpiński triangle #4

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Sierpiński triangle animated

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(Static image)

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The 2×2 square seems too simple for anything more, but there’s a simple way to enrich it: label the corners of the sub-squares so that you can, as it were, individually rotate them 0°, 90°, 180°, or 270°. One set of rotations produces the hourglass fractal, like this:

Hourglass stage 1

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Hourglass #2

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Fractal #3

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Hourglass #4

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Hourglass #5

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Hourglass #6

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Hourglass animated

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(Static image)

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Here are some more fractals from the 2×2 square created using this technique (I’ve found some of them previously by other routes):

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