Query to find out rows deleted from a table

WITH test AS (SELECT '1' id
              FROM DUAL
              UNION ALL
              SELECT '2' id
              FROM DUAL
              UNION ALL
              SELECT '4' id
              FROM DUAL
              UNION ALL
              SELECT '5' id
              FROM DUAL
              UNION ALL
              SELECT '6' id
              FROM DUAL)
SELECT TO_CHAR (l)
FROM (SELECT LEVEL l
      FROM DUAL
      CONNECT BY LEVEL <= (SELECT MAX (id)
                           FROM test))
MINUS
SELECT id
FROM test 

SELECT TO_CHAR (l)
FROM (SELECT LEVEL l
      FROM DUAL
      CONNECT BY LEVEL <= (SELECT MAX (id)
                           FROM <YOUR_TABLE>))
MINUS
SELECT id
FROM <YOUR_TABLE>

WITH recursive t(Val) AS (
values(1),(2),(4),(5),(6),(12)),
rec(Val,LeadVal) as(
select Val+1,LeadVal
  from (select Val,Lead(Val) over(order by Val) as LeadVal
          from t) tmp
 where Val+1 < LeadVal
union all
select Val+1,LeadVal
  from rec
 where Val+1 < LeadVal)
select Val from rec;

 val
-----
   3
   7
   8
   9
  10
  11