12
Haiku: 5/7/5 tanka: 5/7/5/7/7
-5
7 squared is 49 and 5 squared is 25. So the difference is 49-25=24
7 and 2 are the prime numbers having a difference of 5.
It's hard to explain without using the word difference, but here's an example: The difference between 5 and 7 is 2. 7 minus 5 = 2