See the documentation about managing identity columns, and identity gaps at:
http://infocenter.sybase.com/help/topic/com.sybase.infocenter.dc32300.1570/html/sqlug/X35353.htm
Also, I would take this opportunity to point out that identity columns are not the same as "sequences". Although identity columns will always increase, they are only guaranteed to be unique. The fact that you "expect" a particular value after an insert isn't consistent with the implementation here.
