Hi Sudarsan
All the objects related to workflow (standard task, workflow tasks and others) are assigned a eight digit number. The prefix number is used for the first 3 digits and the rest five is automatically assigned by the system (starting with 00001).
For example , workflow consists of 8 digits (00500001), first 3 digits 005 has to be maintained as Prefix number for workflows and last 5 numbers(00001) should be automatically picked by system during work flow customization.
Balajee