A two-digit number $AB$ is called a symmetric prime if both $AB$ and $BA$ are prime numbers. For a symmetric prime number $AB$, which of the following cannot be the product A.B? A) 7 B) 9 C) 15 D) 21 E) 63
A two-digit number $AB$ is called a symmetric prime if both $AB$ and $BA$ are prime numbers.
For a symmetric prime number $AB$, which of the following cannot be the product A.B?\\
A) 7\\
B) 9\\
C) 15\\
D) 21\\
E) 63