47.
It is 37.
37
Greatest . . . 37 Smallest . . . 23
19 x 41 = 779
It is: 37
42
The greatest prime factor of 40 is: 5
37 is a prime number between 30 and 40.
47 - 31 = 16
37
The greatest prime factor of 40 is 5. The greatest prime factor of 63 is 7. They do not have any prime factors in common.
There are two prime numbers between 30 and 40 - these are 31 and 37.