How many unique IDs does the random number of the last 3 bytes of mongodb ObjectId support?

  mongodb, question

What is described in the book is that at most 2563(16 777 216) different ObjectId are allowed per process in the same second. The maximum 24-bit random number is 16777216, but why is it in brackets and how is 2563 outside the brackets calculated?

This book is funny, the format was lost when it was copied.
Is 256 3, that is2^(8*3)=2^24
I found this number in Baidu search can find many articles without brain copy, the quality of Chinese blog is worrying.