What's an equation that describes a circle, with oscillating outline? I'm looking for an equation that describes a circle with oscillating outline. See picture below. Anyone who knows a good way to do that? ![sketch of the intended result]( Thanks a lot!

In polar coordinates, add some periodic perturbation to a constant radius. E.g.

$$\rho=R+r\cos(n\theta).$$

![enter image description here](