Primitive recursive ordinal function

A primitive recursive ordinal function is a way of assigning numbers to different objects to tell us how many there are. Let's say we have pencils of different colors. We can use the primitive recursive ordinal function to give each pencil a number, starting with the first color pencil being number 0, the second being number 1, and so on. This way, we can easily see how many pencils there are by looking at how high the last number is.