declare
a varchar2(100) :=  '10,11,12,13';
c dbms_utility.uncl_array;
l_tablen  NUMBER;
I NUMBER;
begin
dbms_utility.comma_to_table(a,l_tablen,c);
FOR I IN C.FIRST..C.LAST LOOP
    DBMS_OUTPUT.put_line(C(I));
END LOOP;
DBMS_OUTPUT.put_line(l_tablen);
exception when others then
DBMS_OUTPUT.put_line( sqlerrm);
end;

--ORA-00931: missing identifier

DECLARE
a varchar2(100) :=  '"1","3","5","7"';
c dbms_utility.uncl_array;
l_tablen  NUMBER;
I NUMBER;
BEGIN
a:=TO_CHAR(a);
dbms_utility.comma_to_table(a,l_tablen,c);
FOR I IN C.FIRST..C.LAST LOOP
    DBMS_OUTPUT.put_line(rtrim(ltrim(C(I),'"'),'"'));
END LOOP;
DBMS_OUTPUT.put_line('Count is: '||l_tablen);
end;

1
3
5
7
Count is: 4

PL/SQL procedure successfully completed.

SQL> declare
  2  a varchar2(100) :=  'a10,a11,a12,a13';
  3  c dbms_utility.lname_array;
  4  l_tablen  NUMBER;
  5  I NUMBER;
  6  begin
  7  dbms_utility.comma_to_table(a,l_tablen,c);
  8  FOR I IN C.FIRST..C.LAST LOOP
  9      DBMS_OUTPUT.put_line(C(I)||' -> '||substr(C(I),2));
 10  END LOOP;
 11  DBMS_OUTPUT.put_line(l_tablen);
 12  end;
 13  /
a10 -> 10
a11 -> 11
a12 -> 12
a13 -> 13
 ->
4