Number Theory

# Identifying Primes

What is the next prime number in this sequence:

$2, 3, 5, 7, 11, 13, \underline{\quad}, \ldots ?$

True or false: the number $47$ is prime.

Which of the following numbers is prime?

$A, \hspace{0.5cm} A+2, \hspace{0.5cm} A+4$

If $A>3,$ can all three numbers above be prime?

True or false: the number $21$ is prime.

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