This is expected behaviour in OSM 7.2, OSM will not use oracle sequence id for creating the order id's. For more information, please refer the OSM 7.2 release notes.
See OSM 7.2 release notes.
Order ID Generation
OSM 7.2 uses a new order ID generation mechanism. Each database server instance allocates order IDs in blocks. The instance then provides an order ID to each newly created order from the block, When all order IDs from the block are used, a new block is allocated. The overhead normally incurred by each instance to allocate sequence numbers such as the order ID one at a time and synchronize with other instances is avoided.
The allocated size of each order ID block matches the size of a database range-partition. In most cases, the database instances in an active-active Oracle RAC configuration work with their own database partition.
Note that in active-active Oracle RAC deployments the order IDs generated are out of sequence because each of the Oracle RAC instances uses different ranges of order IDs.
Orders are getting skipped to 1000000 :
This is known issue in OSM. To avoid this issue, oracle recommends the customers to set "deferred_segment_creation to true". Orders will not skip to 1000000 orders. Also, partition size should be as less as possible to avoid big difference in the order id's.
EX: by default, osm installer shows 1000000 as a default partition value, please keep this value low to avoid big difference in the order id's.