When using double hashing, the second hash function is defined as $$h_2(x)=A-x\mod A,$$ where $A$ is a prime number less than the capacity of the hash table. But why must $A$ be a prime number?
(This differs from Why is it best to use a prime number as a mod in a hashing function? because the prime number in question is the constant of the second hash function in a double hashing table, whereas the prime number in the other question is the mod of the hash table. In addition, it seems not that significant to avoid collisions because the second hash function in double hashing is used to determine the "jump size".)