Oracle Database Discussions

Hi,

One of our customer is hitting the max sequence number ( around 1.2Billion). However on analysis we noticed they have used only 3% of the sequence numbers in the actual data. Other sequence number is wasted due to purge or data recreation. So we are trying to find out if there is way to reuse them.

Questions
a) Do you have any suggestions how to reuse the sequences ( Unused sequence)?
b) Does Oracle Database allow some custom code while deriving the sequence number, i.e some logic based sequence numbers?

Thanks,
Hussain