Factorial Calculator (n!)
n factorial (n!) is the product of all whole numbers from 1 to n; 5! = 5 × 4 × 3 × 2 × 1 = 120, and 0! is defined as 1.
At a glance
| What it is | Free factorial calculator: n! = n × (n − 1) × … × 1. 0! = 1, 5! = 120, 10! = 3,628,800. Also combinations nCr. Instant answers. |
|---|---|
| Type | Interactive guide with a calculator |
| Level | High school and college |
| Price | Free, with no account or sign-up |
| Works offline | Yes, after the first visit; installs as an app |
| Made by | Aalok (aalok.builds@gmail.com) |
| Last updated | 1 November 2026 |
Key facts
| Definition | n! = n × (n − 1) × … × 2 × 1 |
|---|---|
| Special case | 0! = 1 |
| Values | 5! = 120, 10! = 3,628,800, 20! ≈ 2.43 × 10¹⁸ |
| Combinations | nCr = n! ÷ (r! (n − r)!) |
| Permutations | nPr = n! ÷ (n − r)! |
Where are factorials used?
Factorials count arrangements: 5 books can be arranged on a shelf in 5! = 120 ways. They also appear in combinations, probability and series.
How to use it in Plotline
- 10! is already entered; its answer shows next to the input.
- Type a number followed by the n! key.
- For combinations use the nCr function on the graphing keypad, or the formula above.
Frequently asked questions
Why is 0! equal to 1?
There is exactly one way to arrange zero objects, and defining 0! = 1 keeps formulas such as nCr = n! ÷ (r!(n − r)!) working for r = 0 and r = n.
Is it free?
Yes. The scientific calculator is free with no account and no sign-up, and every function is available: logs, roots, trigonometry, factorials, powers and constants. It installs as an app on a phone or computer and works offline.
Learn more
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