Mesopotamia is an ancient region located in the eastern Mediterranean, primarily corresponding to parts of modern-day Iraq, as well as parts of Syria and Turkey. If you are looking for a numerical representation such as a region number, it might depend on the specific classification system being used (like in educational materials or geographic databases). For example, in some contexts, the broader Middle East may be represented by certain region codes or numbers.
If you provide more context about what you mean by "number," I may be able to give a more precise answer.