with test as
      (select '421907802490;421907672085;421911460415;421905464170;421907802292' col from dual)
    select regexp_substr(col, '[^;]+', 1, level) result
    from test
    connect by level <= length(regexp_replace(col, '[^;]+')) + 1; 

WITH tmptab AS
(
    SELECT '421907802490;421907672085;421911460415;421905464170;421907802292'
    AS colval FROM DUAL 
    UNION
    SELECT '111111111;222222222;333333333333;4444;55555555555' FROM DUAL
)
SELECT  REGEXP_SUBSTR(t1.colval, '([^;])+', 1, t2.COLUMN_VALUE)
FROM tmptab t1 CROSS JOIN
            TABLE
            (
                CAST
                (
                    MULTISET
                    (
                        SELECT LEVEL
                        FROM DUAL 
                        CONNECT BY LEVEL <= REGEXP_COUNT(t1.colval, '([^;])+')
                    )
                    AS SYS.odciNumberList
                )
            ) t2;


REGEXP_SUBSTR(T1.COLVAL,'([^;])+',1,T2.COLUMN_VALUE)
----------------------------------------------------------------
111111111
222222222
333333333333
4444
55555555555
421907802490
421907672085
421911460415
421905464170
421907802292

10 rows selected.

SQL>