# Multifactorial Calculator

## Calculator Use

Calculate the following factorials. Note that n!!, and similarly to other multifactorials, is not the same as (n!)!. Refer to formulas below.

- factorial n!
- double factorial n!!
- triple factorial n!!!
- quadrupal factorial n!!!!
- quintuple factorial n!!!!!

## Factorial Formula

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

Factorial of 5

5! = 5 × 4 × 3 × 2 × 1 = 120

## Double Factorial Formula

n!! = n × (n - 2) × (n - 4) × (n - 6) × ...

Double Factorial of 10

10!! = 10 × 8 × 6 × 4 × 2 = 3,840

Note that some programming languages use the function dfactorial to compute double factorials.

## Triple Factorial Formula

n!!! = n × (n - 3) × (n - 6) × (n - 9) × ...

Triple Factorial of 22

22!!! = 22 × 19 × 16 × 13 × 10 × 7 × 4 × 1 = 24,344,320

#### References

[1] For more information on double, triple and quadruple factorials please see the Multifactorial page at Wolfram MathWorld.