help me out of this query

[tamilselvan]

SQL> set echo on feedba on
SQL> get cr_fn
  1  create or replace function num2word(num in number)
  2    return varchar2
  3    as
  4    begin
  5    return  to_char(to_date(num, 'j'),'JSPTH');
  6*  END;
  7  /

Function created.

SQL> select num2word(987654321) from dual;
select num2word(987654321) from dual
       *
ERROR at line 1:
ORA-01854: julian date must be between 1 and 5373484
ORA-06512: at "SYS.STANDARD", line 167
ORA-06512: at "OPS$ORACLE.NUM2WORD", line 5