Factorials are used eg. in probability (combinatorics) and set theory. A factorial is the number of different ways you can combine a specific number of elements. Eg three elements can be combined in six different ways.
Example: 3! = 3 * 2 * 1
| Integer (n) | Fact (n!) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 5 040 |
| 8 | 40 320 |
| 9 | 362 880 |
| 10 | 3 628 800 |
| 11 | 39 916 800 |
| 12 | 479 001 600 |
| 13 | 6 227 020 800 |
| 14 | 87 178 291 200 |
| 15 | 1 307 674 368 000 |
| 16 | 20 922 789 888 000 |
| 17 | 355 687 428 096 000 |
| 18 | 6 402 373 705 728 000 |
| 19 | 121 645 100 408 832 000 |
| 20 | 2 432 902 008 176 640 000 |
More:
21! = 21 * 20!
22! = 22 * 21!
23! = 23 * 22!
...