Prime numbers are special numbers that can only be divided by themselves and 1.
19 is a prime number. It can only be divided by 1 and 19.
The number 1 is not thought of as a prime number.
9 is not a prime number. It can be divided by 3 as well as 1 and 9.
The prime numbers below 20 are:
2, 3, 5, 7, 11, 13, 17, 19
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