# The Excel FACTDOUBLE Function

Double Factorial

The Double Factorial of a number, N, is given by the following:

If N is even:

N * (N-2) * (N-4) * ... * 4 * 2

If N is odd:

N * (N-2) * (N-4) * ... * 3 * 1

For further details, see the Wikipedia Factorial page

Related Function:
FACT Function

## Function Description

The Excel Factdouble function returns the double factorial of a supplied number.

The syntax of the function is:

FACTDOUBLE( number )

where the number argument is the positive integer that you want to calculate the double factorial of.

## Factdouble Function Examples

Cells A1-A3 of the following spreadsheet shows examples of the Excel Factdouble function, used to calculate the double factorial of the integers 5, 8 and 13.

Formulas:
AB
1=FACTDOUBLE( 5 )= 5 x 3 x 1
2=FACTDOUBLE( 8 )= 8 x 6 x 4 x 2
3=FACTDOUBLE( 13 )= 13 x 11 x 9 x 7 x 5 x 3 x 1
Results:
AB
115= 5 x 3 x 1
2384= 8 x 6 x 4 x 2
3135135= 13 x 11 x 9 x 7 x 5 x 3 x 1

Further examples of the Excel Factdouble function are provided on the Microsoft Office website.

## Excel Factdouble Function Errors

If you get an error from the Excel Factdouble function this is likely to be one of the following:

Common Errors
 #NUM! - Occurs if the supplied number is < 0. #VALUE! - Occurs if the supplied number is non-numeric.