how Hash Code Combinations works and what is this

I have a hash code but I don't know how it works. I have a table. the table keeps all permute that created by (A,C,T,G) with 1 to 7 length. The location of the letters in each row of the table is important for example ACT is different from ATC. the program uses a bellow formula to create a hash table. but I can't understand how it works

Hash(x) = ((hash * 16223) ^ int(x) % 50021   );
 

that code is in c