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Hauts-de-Seine (French pronunciation: [o d(ə) sɛn] ; lit. 'Seine Heights') is a department in the Île-de-France region of France. It covers Paris's western inner suburbs. It is bordered by Paris, Seine-Saint-Denis and Val-de-Marne to the east, Val-d'Oise to the north, Yvelines to the west and Essonne to the south. With a population of 1,624,357 (as of 2019) and a total area of 176 square kilometres (68 square miles), it has the second highest population density among all departments of France, after Paris. It is the fifth most populous department in France. Its prefecture is Nanterre, but Boulogne-Billancourt, one of its two subprefectures, alongside Antony, has a larger population.
Hauts-de-Seine is best known for containing the modern office, cinema and shopping complex La Défense, one of Grand Paris's main economic centres and one of Europe's major business districts. Hauts-de-Seine is one of the wealthiest departments in France; it had the highest GDP per capita in France at €107,800 in 2020. Its inhabitants are called Altoséquanais (masculine) and Altoséquanaises (feminine) in French.