# FACTDOUBLE

The FACTDOUBLE function returns the double factorial of a number, which is the product of every second number up to the given number.

## Syntax

=FACTDOUBLE(`number`

)

`number` | The number for which you want to calculate the double factorial. |

## About FACTDOUBLE

When you need to calculate the double factorial of a number in Excel, turn to FACTDOUBLE. This nifty function provides an efficient way to find the product of every second number up to the specified value. Whether you're dealing with permutation problems or combinatorial calculations, FACTDOUBLE simplifies the process by swiftly computing the double factorial result with ease and accuracy. It's a useful tool for mathematical operations where the concept of a double factorial is relevant, offering a convenient solution for obtaining precise numerical outcomes.

## Examples

For example, if you want to find the double factorial of 8, you would use the formula: =FACTDOUBLE(8). This will return the result of 3840, which is the product of every second number starting from 8 down to 1 (8*6*4*2 = 3840).

Another example could be calculating the double factorial of 5 using the formula: =FACTDOUBLE(5). This will give you the answer of 15 (5*3*1 = 15).

## Questions

**What is the significance of the double factorial in mathematical calculations?**

The double factorial is commonly used in combinatorial mathematics, particularly when dealing with permutations and arrangements. It helps efficiently calculate the product of every second number up to a given value, providing a specialized tool for specific mathematical computations.

**Can I use negative numbers or non-integer values with the FACTDOUBLE function?**

No, the FACTDOUBLE function works with positive integers only. It is designed to calculate the double factorial of whole numbers, starting from the provided input number and descending by twos until reaching 1.

**How does the FACTDOUBLE function differ from the FACT function in Excel?**

The FACT function calculates the factorial of a number by multiplying all positive integers up to that number, while the FACTDOUBLE function specifically computes the double factorial by multiplying every second number up to the specified value. The distinction lies in the pattern of multiplication followed by each function.

## Related functions

FACT

COMBIN

PERMUT