Computing hash of a compound key Why is the initial value of hash 17 and not 0?

/**
 * Returns an integer hash code for this date.
 *
 * @return an integer hash code for this date
 */
@Override
public int hashCode() {
    int hash = 17;
    hash = 31*hash + month;
    hash = 31*hash + day;
    hash = 31*hash + year;
    return hash;
}


https://algs4.cs.princeton.edu/code/edu/princeton/cs/algs4/Date.java.html
There is no compelling reason that I'm aware of.  The hash algorithm would also work about as well with an initial value of 0, as far as I can see.