CREATE SEQUENCE supplier_seq
    MINVALUE 1
    MAXVALUE 999999999999999999999999999
    START WITH  1
    INCREMENT BY  1
    CACHE 20;

This would create a sequence object called supplier_seq.  The first sequence number that it would use is 1 and each subsequent number would increment by 1 (ie: 2,3,4,...}.  It will cache up to 20 values for performance.

Now that you've created a sequence object to simulate an autonumber field, we'll cover how to retrieve a value from this sequence object.  To retrieve the next value in the sequence order, you need to use nextval.

For example:

supplier_seq.nextval

This would retrieve the next value from supplier_seq

INSERT INTO suppliers
(supplier_id, supplier_name)
VALUES
(supplier_seq.nextval, 'Kraft Foods');