There is a table m1 which contains serial as:
1
2
4
5

Expected result: The report should show the serial 3.

SQL> select * from m1;

    SERIAL
----------
         1
         2
         4
         5
         8
         9

6 rows selected.

SQL> select level
  2  from dual
  3  connect by level <= (select max(serial) from m1)
  4  minus
  5  select serial
  6  from m1;

     LEVEL
----------
         3
         6
         7

SQL>