Drucker, Peter Ferdinand, 1909-2005
America's next twenty years
Harper & Brothers, 1957
 Buku Teks
Davidson, Jamie S.
Indonesia: twenty years of democracy
Cambridge University Press, 2018
 Buku Teks
Celebrating twenty years with Deloitte in Indonesia
Deloitte Touche Tohmatso limited
Deloitte Touche Tohmatso limited, 2010
 Buku Referensi
Ide Anak Agung Gde Agung, 1921-1999
Twenty years Indonesia foreign policy 1945-1965
Mouton, 1973.
 Buku Teks
Karpinski, Andrzej
Twenty years of Poland's economic development 1944-1964
Polonia Publishing House, 1964
 Buku Teks