Population of a Capital City? Which One?

There are 196 internationally recognized sovereign states, each with a capital city (some have multiple). Populations range from Vatican City (~800) to Beijing (~21.5 million) or Tokyo metro (~37 million). To get a specific figure, you must name the capital—e.g., Washington, D.C. (~670k), London (~9M), Canberra (~460k), Ottawa (~1M).