In this comprehensive guide, we will explore the FACTDOUBLE function in Excel, which calculates the double factorial of a given number. The double factorial is the product of all the integers from 1 to the input number with the same parity (odd or even) as the input number. This function is particularly useful in combinatorics, probability, and advanced mathematics. We will cover the syntax, examples, tips and tricks, common mistakes, troubleshooting, and related formulae for the FACTDOUBLE function.


The syntax for the FACTDOUBLE function in Excel is quite simple:


Where number is the non-negative integer for which you want to calculate the double factorial. The function will return the double factorial of the given number.


Let’s go through some examples to better understand the use of the FACTDOUBLE function in Excel.

Example 1: Calculate the double factorial of 5.


In this example, the function will return 15, as the double factorial of 5 is 5 * 3 * 1 = 15.

Example 2: Calculate the double factorial of 6.


In this example, the function will return 48, as the double factorial of 6 is 6 * 4 * 2 = 48.

Example 3: Calculate the double factorial of 0.


In this example, the function will return 1, as the double factorial of 0 is defined as 1.

FACTDOUBLE Tips & Tricks

Here are some tips and tricks to help you use the FACTDOUBLE function more effectively:

  1. Remember that the FACTDOUBLE function only accepts non-negative integers as input. If you provide a decimal or negative number, the function will return an error.
  2. Use the IFERROR function to handle errors gracefully when using the FACTDOUBLE function. For example:

=IFERROR(FACTDOUBLE(A1), “Invalid input”)

This formula will return “Invalid input” if the value in cell A1 is not a non-negative integer.

Common Mistakes When Using FACTDOUBLE

Here are some common mistakes users make when using the FACTDOUBLE function:

  1. Using decimal or negative numbers as input, which will result in an error.
  2. Confusing the FACTDOUBLE function with the FACT function, which calculates the regular factorial of a number.
  3. Not handling errors properly, which can lead to unexpected results or error messages in your worksheet.

Why Isn’t My FACTDOUBLE Working?

If your FACTDOUBLE function isn’t working as expected, consider the following troubleshooting steps:

  1. Check the input value to ensure it is a non-negative integer. If not, correct the input or use the IFERROR function to handle errors.
  2. Make sure you are using the correct function (FACTDOUBLE) and not the regular FACT function.
  3. Ensure that your formula is entered correctly, with the correct syntax and parentheses.

FACTDOUBLE: Related Formulae

Here are some related formulae that you might find useful when working with the FACTDOUBLE function:

  1. FACT: Calculates the factorial of a given number. Syntax: =FACT(number)
  2. COMBIN: Calculates the number of combinations for a given number of items. Syntax: =COMBIN(number, number_chosen)
  3. PERMUT: Calculates the number of permutations for a given number of items. Syntax: =PERMUT(number, number_chosen)
  4. GAMMALN: Calculates the natural logarithm of the gamma function for a given number. Syntax: =GAMMALN(number)
  5. IFERROR: Returns a custom result or message if a formula generates an error. Syntax: =IFERROR(value, value_if_error)

By understanding the FACTDOUBLE function and its related formulae, you can perform advanced mathematical calculations and solve complex problems in Excel. Remember to use the correct syntax, handle errors properly, and explore related functions to enhance your Excel skills.


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