19
Greatest . . . 37 Smallest . . . 23
5 is the greatest prime factor of 20.
26
19 x 41 = 779
No. The greatest common divisor for 15 and 20 is five. Five is a prime number.
The greatest prime number less than 20 is 19. For there to be a difference, we'll have to have another value.
26
47 is the largest prime number between 20 and 50.
19.
19
23 is the only prime number between 20 and 29.
23 is the only prime number between 20 and 28.