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FACTDOUBLE Function

Excel 2007+

Summary

The FACTDOUBLE function calculates the double factorial of a number, multiplying it by every second positive integer down to either 2 (for even numbers) or 1 (for odd numbers). This specialized math function is essential for advanced statistical calculations and combinatorial analysis.

Syntax

FACTDOUBLE(number)

Parameters

Parameter Type Required Description
number Number Yes The number for which to calculate the double factorial. Non-integers are truncated to integers.

Using the FACTDOUBLE Function

FACTDOUBLE is used in advanced mathematics, particularly in combinatorics, statistics, and probability where double factorials appear in formulas for permutations, series expansions, and special functions. For even n, it computes n × (n-2) × (n-4) × ... × 2. For odd n, it computes n × (n-2) × (n-4) × ... × 1.

Common FACTDOUBLE Examples

Double Factorial of Even Number

=FACTDOUBLE(6)

Calculates 6!! = 6×4×2 = 48. Demonstrates even number calculation.

Double Factorial of Odd Number

=FACTDOUBLE(7)

Calculates 7!! = 7×5×3×1 = 105. Shows odd number computation.

Using Cell Reference

=FACTDOUBLE(A1)

Calculates double factorial of value in cell A1, useful for dynamic calculations.

Frequently Asked Questions

FACTDOUBLE truncates non-integer values to the nearest lower integer before calculation.

FACTDOUBLE(0) returns 1 and FACTDOUBLE(1) returns 1, following double factorial conventions.

FACT calculates regular factorial (n!), while FACTDOUBLE calculates double factorial (n!!).

Common Errors and Solutions

#VALUE!

Cause: Number argument is non-numeric

Solution: Ensure the number parameter contains a valid numeric value

#NUM!

Cause: Number argument is negative

Solution: Use only positive numbers or zero

#VALUE!

Cause: Text or logical values passed

Solution: Convert text to numbers using VALUE function

Notes

  • Double factorial for even n: n!! = n × (n-2) × (n-4) × ... × 2
  • Double factorial for odd n: n!! = n × (n-2) × (n-4) × ... × 1
  • 0!! = 1 and 1!! = 1 by definition
  • Available in Excel 2007 and later versions

Compatibility

Available in: Excel 2007, Excel 2010, Excel 2013, Excel 2016, Excel 2019, Excel 2021, Microsoft 365

Not available in: Excel 2003 and earlier

Content last reviewed: December 9, 2025
Update frequency: As needed
Excel versions tested: Excel 2007+