Sumatra is the largest island in Indonesia, but the national capital (Jakarta) is on the island of Java. There are 10 provinces on Sumatra and each province has a capital city:
Nangroe Aceh Darussalam : Banda Aceh
Sumatera Utara : Medan
Sumatera Barat : Padang
Riau : Pekanbaru
Jambi : Kota Jambi
Sumatera Selatan : Palembang
Bengkulu : Bengkulu Kota
Lampung : Bandar Lampung
Kepulauan Bangka Belitung : Pangkal Pinang
Kepulauan Riau : Tanjung Pinang
The capitol of Sumatra is the city of Jakarta.