The `FACTDOUBLE` function in Excel is used to calculate the double factorial of a non-negative integer. The double factorial of a number n (denoted as n!!) is the product of all the integers from 1 up to n that have the same parity (odd or even) as n. For example, if n is even, the double factorial would be n × (n-2) × (n-4) × … × 2; if n is odd, it would be n × (n-2) × (n-4) × … × 1.
Here is how you can use the `FACTDOUBLE` function in Excel:
Syntax
FACTDOUBLE(number)
- number: This is the integer for which you want to compute the double factorial. It must be a non-negative integer. If the number is not an integer, it will be truncated to an integer.
Steps to Use
- Select a Cell: Click on the cell where you want the result to appear.
- Enter the Formula: Type the formula `=FACTDOUBLE(number)` into the cell. Replace `number` with the cell reference or the actual non-negative integer value for which you want to calculate the double factorial.
- Press Enter: After typing the formula, press Enter to get the result.
Example
Suppose you want to find the double factorial of 8:
- Click on a cell (e.g., A1).
- Type `=FACTDOUBLE(8)`.
- Press Enter, and the cell will display `384`, since 8!! = 8 × 6 × 4 × 2.
Notes
- If `number` is less than 0, `FACTDOUBLE` will return a `#NUM!` error.
- If `number` is not numeric, the function will return a `#VALUE!` error.
This function is particularly useful in combinatorial algorithms and certain mathematical problems where double factorials are involved.
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