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List of prime numbers before 21

Here is the answer to questions like: List of prime numbers before 21. Get all the prime numbers from one to 21. Use the Prime Numbers Before Calculator below to discover if any given number is prime or composite and get all the primes up to 21.

Prime Numbers Before Calculator

Enter a natural number to calculate the primes before it:
Ex.: 4, 11, 64, 128, ... until 10,000.
 

Prime Numbers Before 21:

The number 21 is not a prime number because it is possible to express it as a product of prime factors. In other words, 21 can be divided by 1, by itself and at least by 3 and 7. So, 21 is a 'composite number'.

List of prime numbers before 21:

2, 3, 5, 7, 11, 13, 17, 19.

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