What country does the island Sumatra belong to?

Explanation

Sumatra is an island in the western part of Indonesia. It is the second largest island in Asia (only Borneo is larger) and the 6th largest in the world. It covers an area of approximately 470,000 km2. The island is the fourth most populated island in the world. Sumatra was known in ancient times by the Sanskrit names of Swarnadwīpa ("Island of Gold") and Swarnabhūmi ("Land of Gold").