table continued item number key hash value step size cells in probe sequence the first keys mostly hash to vacant cell (the th one is an anomalyafter thatas the array gets more fullthe probe sequences become quite long here' the resulting array of keys* * table size prime number double hashing requires that the size of the hash table is prime number to see whyimagine situation in which the table size is not prime number for examplesuppose the array size is (indices from to )and that particular key hashes to an initial index of and step size of the probe sequence will be and so onrepeating endlessly only these three cells are ever examinedso the algorithm will never find the empty cells that might be waiting at and so on the algorithm will crash and burn if the array size were which is primethe probe sequence will eventually visit every cell it' and so on and on if there is even one empty cellthe probe will find it using prime number as the array size makes it impossible for any number to divide it evenlyso the probe sequence will eventually check every cell