can a Car Registration Number, a combination of prime, be prime? While waiting in my car, I noticed registration number of a car parked in front of my car was 6737. So it was a concatenation of two prime numbers 67 and 37.
Now I know following ways to check whether any number is prime or not
Let $p$ be the number to be checked for being prime or not
1) if p is divided by any prime in between 2 to $\sqrt[2]{(p)}$ 
then it is not a prime.
2) $\forall i ; 1< i < p $ if p mod i equals $0$ then the number is not prime.
Do we have s method so that we can check whether combination of prime numbers (here 67 and 37) constitutes prime number (6737) or not ?

This is true for the prime numbers 3, 7, 109 and 673 that if you concatenate any  two of these numbers in any order , the resulting number will be a prime ; as in this case Concatenating 7 at the end of 673 resulting in 6737 which is a prime . Concatenating 7 in the front of 673, which gives 7673 , is also a prime . So is 1093, 1097, 3109, 7109.
