declare
  n number;
  temp number;
  sum number := 1;
begin
  n := &n;
  temp := n;
  while temp>0 loop
    sum := temp*sum;
    temp := temp-1;
  end loop;
  dbms_output.put_line('Factorial of '||n||' is '||sum);
end;
/

declare
  n number;
  temp number;
  sum_ number := 1;
begin
  n := &n;
  temp := n;
  while temp>0 loop
    sum_ := temp*sum_;
    temp := temp-1;
  end loop;
  dbms_output.put_line('Factorial of '||n||' is '||sum_);
end;
/

select round(exp(sum(ln(level))))
from dual
connect by level <= 5;

create or replace package test_ is

  function by_query(num number) return number deterministic;

  function by_plsql(num number) return number deterministic;

end test_;

/

create or replace package body test_ is

  function by_query(num number) return number deterministic
    is
      res    number;
  begin
    select round(exp(sum(ln(level))))
    into res
    from dual
    connect by level <= num;

    return res;
  end;

  function by_plsql(num number) return number deterministic
    is
      n number := 0;
  begin
    for i in 1..num loop
      n := n + ln(i);
    end loop;

    return round(exp(n));
  end;

end test_;

declare
  dummy   number;
begin
  for i in 1..10000 loop
    dummy := test_.by_query(5);
  end loop;
end;

declare
  dummy   number;
begin
  for i in 1..10000 loop
    dummy := test_.by_plsql(5);
  end loop;
end;

declare
    n number;
    i number;
    sum_of_log_10s number;
    exponent number;
    base number;

begin
    n := &n;

    i := 1;
    sum_of_log_10s := 0;

    while i <= n loop
        -- do stuff
        sum_of_log_10s := sum_of_log_10s + log(10,i);
        i := i + 1;
    end loop;

    dbms_output.put_line('sum of logs = '||sum_of_log_10s);

    exponent := floor(sum_of_log_10s);

    base := power(10,sum_of_log_10s - exponent);

    dbms_output.put_line(n||'! = '||base||' x 10^'||exponent);

end;

ALTER SESSION FORCE PARALLEL DDL PARALLEL 16;
ALTER SESSION FORCE PARALLEL DML PARALLEL 16;
ALTER SESSION FORCE PARALLEL QUERY PARALLEL 16;

with t as (
    select /*+materialize*/
        rownum i
    from dual connect by rownum < 100000 -- put number to calculate n! here
)
,t1 as (
    select /*+parallel(t,16)*/ /*+materialize*/
        sum(log(10,i)) logsum
    from t
    )
select
    trunc(power(10,(mod(logsum,1))),3) ||' x 10^'||trim(to_char(floor(logsum),'999,999,999,999')) factorial
--  logsum
from t1
;

FUNCTION Factorial(num INTEGER) return NUMBER deterministic is
n NUMBER := num;
--
begin
  for i in REVERSE 2..num-1 loop
    n := n * i;
  end loop;
  --
  return n;
end Factorial;