--First create a table according to your requirements. e.g.,

CREATE TABLE Temp_Table
(ID number(6),
NAME varchar2(20));

--Then create a SEQUENCE that generates sequentially generated numbers starting with 100000. e.g.,

CREATE SEQUENCE SEQ_Temp_Table START WITH 100000 nocache
/

--Now create a FUNCTION which return the next value to be inserted into your table. e.g.,

CREATE FUNCTION Temp_Table_NEXT_ID RETURN NUMBER IS
X NUMBER;
BEGIN
SELECT SEQ_Temp_Table.NextVal INTO X FROM DUAL;
RETURN X;
END;
/

--Then INSERT your records. e.g.,

INSERT INTO Temp_Table Values
(Temp_Table_NEXT_ID , 'MYNAME');

I think this should work.

Hope this helps.