Which Greek letter is commonly used to represent a count?

Question

Which Greek letter is commonly used to represent a count? For example, the Greek letter sigma ($\Sigma$) is commonly used to represent a sum.

Answer 1

While your "count" is quite vague, here is a possibility:

The count of elements in a set:

What symbol gives the count of elements in a set?

The latin letter N is, as pointed out in the comments, also sometimes used.