# 20 Factorial - 20!

Here is the answer to questions like: How many digits are there in 20 factorial? What is the factorial of 20? What is the last digits of factorial of 20? How many trailing zeros in 20 factorial? How many digits are there in 20 factorial? Use the factorial calculator below to find the factorial of any real number between 0 and 10,000.

## What is factorial?

### Definition of factorial

The factorial is a quantity defined any all integer x greater than or equal to 0.

The factorial is the product of all integers less than or equal to x but greater than or equal to 1. The factorial value of 0 is by definition equal to 1. For negative integers, factorials are not defined. The factorial can be seen as the result of multiplying a sequence of descending natural numbers (such as 3 × 2 × 1). The factorial symbol is the exclamation mark !.

### The factorial formula

If n is an natural number greater than or equal to 1, then

n! = n x (n - 1) x (n - 2) x (n - 3) ... 3 x 2 x 1

If p = 0, then p! = 1 by convention.

Example: 6! = 6 x 5 x 4 x 3 x 2 x 1 = 720

## Shortcut to find trailing zeros in a factorial

Trailing zeros are a sequence of zeros in the decimal representation of a number, after which no other digits follow. This video shows how to find the trailing zeros of a factorial easily.

## Table of Factorials until 30

n | n! |
---|---|

1 | 1 |

2 | 2 |

3 | 6 |

4 | 24 |

5 | 120 |

6 | 720 |

7 | 5040 |

8 | 40320 |

9 | 362880 |

10 | 3628800 |

11 | 39916800 |

12 | 479001600 |

13 | 6227020800 |

14 | 87178291200 |

15 | 1307674368000 |

16 | 20922789888000 |

17 | 355687428096000 |

18 | 6402373705728000 |

19 | 121645100408832000 |

20 | 2432902008176640000 |

21 | 51090942171709440000 |

22 | 1124000727777607680000 |

23 | 25852016738884976640000 |

24 | 620448401733239439360000 |

25 | 15511210043330985984000000 |

26 | 403291461126605635584000000 |

27 | 10888869450418352160768000000 |

28 | 304888344611713860501504000000 |

29 | 8841761993739701954543616000000 |

30 | 265252859812191058636308480000000 |