create or replace function factorial(val integer)
return  integer
as
minus1 integer;
product integer;
begin
   dbms_output.enable(10000);
   minus1 := val - 1;
   if ( minus1 > 0 ) 
   then
      --dbms_output.put_line('Entering with = '||val);
      product := val*factorial(minus1);
      --dbms_output.put_line('Exiting with = '||product);
      return product;
   end if;
   return val;
end factorial;

select round(exp(sum(ln(n))))
from (
  select level AS n
  from dual
  connect by level <= &n
)

select round(exp(sum(ln(n))))
from (
  select level AS n
  from dual
  connect by level <= &n
)

SQL>  CREATE OR REPLACE FUNCTION FACTORIAL_1(factstr varchar2 )
  2   RETURN NUMBER AS
  3     new_str VARCHAR2(4000) :=  factstr||'*' ;
  4     fact number := 1 ;
  5   BEGIN
  6
  7      WHILE new_str IS NOT NULL
  8      LOOP
  9        fact := fact * TO_NUMBER(SUBSTR(new_str,1,INSTR(new_str,'*')-1));
 10        new_str := substr( new_str,INSTR(new_str,'*')+1);
 11      END LOOP;
 12
 13      RETURN fact;
 14
 15   END;
 16  /

Function created.

SQL> select  FACTORIAL_1(LTRIM(max(sys_connect_by_path(level,'*')),'*'))  AS FAC
TOR
  2  from dual
  3  connect by level <= 5;

    FACTOR
----------
       120

 SQL> select LTRIM( max(sys_connect_by_path(level,'*')),'*') AS n
  2    from dual
  3    connect by level <= 5;

N
------------------------------
1*2*3*4*5

SQL>

SQL> CREATE OR REPLACE FUNCTION FACTORIAL_2(num NUMBER )
  2  RETURN NUMBER AS
  3    fact number := 1 ;
  4    newnum  number := num ;
  5  BEGIN
  6
  7     WHILE newnum >= 1
  8     LOOP
  9       fact    := fact * newnum;
 10       newnum  :=newnum-1;
 11     END LOOP;
 12
 13     RETURN fact;
 14
 15  END;
 16  /

Function created.

SQL>  select FACTORIAL_2(5) FACTOR from DUAL;

    FACTOR
----------
       120

SQL>

SQL> define N=5
SQL> col prod new_value prod
SQL> select substr(max(sys_connect_by_path(rownum,'*')),2) prod
  2  from dual 
  3  connect by level <= &N
  4  /
PROD
----------------------------------------------------------------
1*2*3*4*5

1 row selected.

SQL> select ' &N! = &prod = '||&prod "Factorial" from dual
  2  /
Factorial
---------------------
 5! = 1*2*3*4*5 = 120

1 row selected.

SQL> select ' &N! = '||val "Factorial"
  2  from (select 1 rn from dual )
  3  model
  4    dimension by (rn)
  5    measures (1 val)
  6    rules 
  7      iterate (&N)
  8      ( val[1] = val[1] * (iteration_number+1) )
  9  /
Factorial
----------------------------------------------
 5! = 120

1 row selected.

Create or replace type prod_type as object ( 
  prod number, 

  static function ODCIAggregateInitialize (sctx IN OUT prod_type) return number, 

  member function ODCIAggregateIterate (
    self  IN OUT prod_type, 
    value IN     number) 
  return number, 

  member function ODCIAggregateTerminate (
    self        IN  prod_type, 
    returnValue OUT number, 
    flags       IN  number) 
  return number, 

  member function ODCIAggregateMerge (
    self IN OUT prod_type, 
    ctx2 IN     prod_type) 
  return number 
); 
/ 

Create or replace type body prod_type is 

  static function ODCIAggregateInitialize (sctx IN OUT prod_type) 
  return number 
  is 
  begin 
    sctx := prod_type (null); 
  return ODCIConst.Success; 
  end; 

  member function ODCIAggregateIterate (
    self  IN OUT prod_type, 
    value IN     number) 
  return number 
  is 
  begin 
    self.prod := nvl(self.prod,1) * value;
  return ODCIConst.Success; 
  end; 

  member function ODCIAggregateTerminate (
    self        IN  prod_type, 
    returnValue OUT number, 
    flags       IN  number) 
  return number 
  is 
  begin 
    returnValue := prod; 
    return ODCIConst.Success; 
  end; 

  member function ODCIAggregateMerge (
    self IN OUT prod_type, 
    ctx2 IN prod_type) 
  return number 
  is 
  begin 
    if ctx2 is not null and ctx2.prod is not null and self.prod is not null
    then
      self.prod := nvl(self.prod,1) * nvl(ctx2.prod,1);
    end if; 
    return ODCIConst.Success; 
  end; 

end; 
/ 

Create or replace function prod (input number) 
return number 
PARALLEL_ENABLE AGGREGATE USING prod_type; 
/ 

SQL> Select ' &N! = '||prod(rownum) "Factorial"  
  2  from dual 
  3  connect by level <= &N
  4  /
Factorial
----------------------------------------------
 5! = 120

1 row selected.

SQL> var x number
SQL> define x =5
SQL> select count(*) FACTORIAL from
  2     (
  3  select level  b
  4   from
  5   (select level n from dual connect by level <= &x ) YourTable
  6   connect by nocycle n != prior n
  7  )where b = &x
  8  ;
old   5:  (select level n from dual connect by level <= &x ) YourTable
new   5:  (select level n from dual connect by level <= 5 ) YourTable
old   7: )where b = &x
new   7: )where b = 5

 FACTORIAL
----------
       120

SQL>