Bulk Data Type Testing Question

What is the best way to determine if col1 contains a convertible number?
Bulk collect? Is there a simple SQL function to handle ORA-01722: invalid number.

Only the values inserted with 2 or -1 will should count.

CREATE TABLE TEST1(COL1 VARCHAR2(4000); BEGIN
   FOR x in 1..1000000
   LOOP

      INSERT INTO TEST1
      SELECT
      CASE mod(dbms_crypto.randomnumber,3)
         WHEN 1 THEN 'ABC'
         WHEN 2 THEN '123'
         WHEN -1 THEN '100.42'
         WHEN 0 THEN '444.4a' -- NULL --
to_char(dbms_crypto.randomnumber)
      ELSE 'BJORK'
      END
      FROM DUAL;