Hash code non-zero initial value - note: I am not asking about primes

The initial value must be a prime number. Why? Because say you are hashing to get an index for an array of length = 20: [object.getHash()%20] is the index of the array where you will want to store your object. If you had used an even number: half of the addresses of your data structure would never be used...this is why you need to use an initial value: to minimize collisions...and maximize data structure usage