If PL/SQL table stores unique whole numbers between -2147483647 and 2147483647 you can use index as the value. For example table with 3 values 12, 120 and 1200 can be populated:

SQL> declare type tbltype is table of boolean index by binary_integer;
2 tbl tbltype;
3 begin
4 tbl(12) := TRUE;
5 tbl(120) := TRUE;
6 tbl(1200) := TRUE;
7 if tbl.exists(12)
8 then
9 dbms_output.put_line('Table contains element with value 12');
10 else
11 dbms_output.put_line('Table does not contain element with value 12');
12 end if;
13 if tbl.exists(17)
14 then
15 dbms_output.put_line('Table contains element with value 17');
16 else
17 dbms_output.put_line('Table does not contain element with value 17');
18 end if;
19 end;
20 /
Table contains element with value 12
Table does not contain element with value 17

PL/SQL procedure successfully completed.

In 9i you can use same logic for any datatype (not just numbers) by using associative arrays.

SY.