- Factorial of
 is defined as  , where is natural number.
 (Permutation)
 (Combination)
 
- For large
 ,  is called Striling Approximation Formula.
 ,  ,  , 
 , 
- If
 is positive integer, then 
- General Term
- If
 is not positive integer, then the binomial expansion is  is called the binomial series. |
