If M is a prime number, the third power of m plus 3 is a prime number, and the seventh power of m plus 7 is a prime number, why?

If M is a prime number, the third power of m plus 3 is a prime number, and the seventh power of m plus 7 is a prime number, why?


If M is prime, there are two cases,
M = 2, then the cubic of m plus three is 11, which is also prime. Then the seventh power of m plus 7 = 135, divided by 5, is a composite number
If M is not equal to 2, then the third power of M is odd, and three is even, so it can't be prime
To sum up, M = 2, the seventh power of m plus seven is 135, which is a composite number