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Prime numbers from 1 to 20

Here is the answer to questions like: Prime numbers from 1 to 20. Get all the prime numbers from one to 20. Use the Prime Numbers Before Calculator below to discover if any given number is prime or composite and get all the primes up to 20.

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 20:

The number 20 is not a prime number because it is possible to express it as a product of prime factors. In other words, 20 can be divided by 1, by itself and at least by 2 and 5. So, 20 is a 'composite number'.

List of prime numbers before 20:

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

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Sample Numbers - Check if they are prime.