How many prime numbers are less than 20?

Related questions

• Are prime numbers infinite?
• Is 81 a prime number?
• Is 0 and 1 a prime number?
• What are prime numbers?
• Is 89 a prime number?
• Is 10 a prime number?
• Is 69 a prime number?
• What is a co-prime number?
• Is 35 a prime number?
• Is 42 a prime number?