What is 21 and 18?

21 and 18 are numbers. 21 is the integer that comes after 20 and before 22, while 18 is the integer that comes after 17 and before 19. Both numbers are commonly used to represent age, as 18 is the legal age of adulthood in many countries and 21 is the legal drinking age in the United States. Additionally, 21 is a Fibonacci number and has several interesting mathematical properties, while 18 is a composite number that can be factored into 2 and 9 or 3 and 6.