Eighteen is a composite number, its proper divisors being 1, 2, 3, 6 and 9.
18 is the age limit for being allowed a driver's license in many parts of the world.
... Informazioni Generali e Sicurezza[?] (SISDE) Servizio per le Informazioni e la Sicurezza Militare[?] (SISMI) Japan Public Security Investigation Agency[?] ...