Sequence to the existing table?

Below are the reasons to generate gap in sequence objects:

1. You have used Sequence number using Cache Option(Default Cache Size is 50.),Below are the possibility of this issues:-

1. When created with the CACHE option, an unexpected shutdown (such as a power failure) may result in the loss of sequence numbers remaining in the cache.

2. Sequence numbers are generated outside the scope of the current transaction. They are consumed whether the transaction using the sequence number is committed or rolled back.