First, you should define your rules about the 'generated alphanumeric sequence numbers'.

after that, I imagine someone
(there is some amazing talent on this board and they are capable of turning water into wine)
can provide a DB2-SQL solution for you.

The first solution provided by ARWinner is no longer applicable because you decided to change the rules of the algorithm.

None of the members are being paid for the time they invest in creating a solution for you.

This is not an easy task, DB2 deals strictly within data types,
and you are mixing two data types in one column,
which means that each char position within the column must be handled in a method that is not inherent to db2,
something an application language can do easily.