# The Sierpinski gasket

So far, the examples of recursion that we've seen require you to make one recursive call each time. But sometimes you need to make multiple recursive calls. Here's a good example, a mathematical construct that is a fractal known as a Sierpinski gasket:
As you can see, it's a collection of little squares drawn in a particular pattern within a square region. Here's how to draw it. Start with the full square region, and divide it into four sections like so:
Sierpinski gasket 2 by 2
Take the three squares with an × through them—the top left, top right, and bottom right—and divide them into four sections in the same way:
Sierpinski gasket 4 by 4
Keep going. Divide every square with an × into four sections, and place an × in the top left, top right, and bottom right squares, but never the bottom left.
Sierpinski gasket 8 by 8
Sierpinski gasket 16 by 16
Sierpinski gasket 32 by 32
Sierpinski gasket 64 by 64
Once the squares get small enough, stop dividing. If you fill in each square with an × and forget about all the other squares, you get the Sierpinski gasket. Here it is once again: