If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Pixar in a Box>Unit 13

Lesson 2: Counting crowds

# 3. Calculating factorials

Factorials represent the product of a series of descending numbers, marked with an exclamation point. For example, 4 factorial (4!) equals 24, because 4 times 3 times 2 times 1 equals 24. The number of permutations can be calculated using the factorial formula!

## Want to join the conversation?

• Do you actually use 10! in Pixar to create robots and if so, how do you narrow your choices down?
Loving these lessons!
• Probably they either chose their favorites or didn't use that many parts...
• I don’t understand this is too hard
• Well since every piece is used oned per snake bot
• I though i was going to have to do the 10 colours for a second
(1 vote)
• i ust realised the lamp.
(1 vote)
• Are there any properties of factorials that would be useful to know, such as dividing them or multiplying them? Thank you!
(1 vote)
• Well say you have 24!, but you only wanted the first few.
Then you can say you want 24x23x22x21. So just do 24! and divide it by 20 factorial and there's your answer (:
You can check more on Numberphile, if you like, I find their videos really helpful ^^
(1 vote)
• Hi!

Here from sigma notation, I'm just curious, sigma notation lets you specify what number you'd like to stop adding. Can factorials do this?

Thanks!
• Is there a mathematical sign that looks like `"?"`?