Plus a PPLC (which I understand) – 2988507 (population 2.14M)
The ADM3 is a child of the ADM2, and the ADM4 a child of the ADM3.
The ADM2 and the PPLC have the same Wikipedia link.
I've always wondered why the ADM3 & ADM4 existed – they seem redundant. Paris is clearly well-known and hence I assume it's been properly reviewed. There must be a good reason for the ADM3/ADM4…
The admin codes drill down in the official administration subdivisions. To paraphrase from the French page:
ADM4 (75056) is the commune of Paris (town/city/village)
… which is part of ADM3 (751) a.k.a. the arrondissement or Paris
… which is part of ADM2 (75), the departement of Paris
… which in turn is part of ADM1 (11), the region Île-de-France