Visible sunspots vary in number according to a cycle of how many years?

On the average, visible sunspots cycle is about eleven years. But there can be variations in the cycle.

Generally, the sun observes a solar cycle of eleven years. In this cycle, there are fluctuations in the activity, such as the ejected levels of solar radiation, and in the appearance of the sun, such as changes in the amount and size of sun spots, solar flares and other phenomena that occur on the sun's surface.

These changes also affect phenomena on earth, especially the auroras.