Skip to content

Fact double

FACTDOUBLE Function

The FACTDOUBLE function in Excel calculates the double factorial of a number. A double factorial of a number is the product of all integers from the specified number down to 1 that have the same parity (even or odd) as the number itself.

Syntax:

FACTDOUBLE(number)
  • number: The non-negative number for which you want to calculate the double factorial. If the number is not an integer, it is truncated.

Examples:

  1. =FACTDOUBLE(6) would return 48, since the double factorial of 6 is 6 * 4 * 2 = 48.
  2. =FACTDOUBLE(7) would return 105, as the double factorial of 7 is 7 * 5 * 3 * 1 = 105.
  3. =FACTDOUBLE(0) returns 1, because the double factorial of 0 is defined as 1.
  4. =FACTDOUBLE(1) also returns 1, since the double factorial of 1 is 1.

Usage Notes:

  • The FACTDOUBLE function can handle only non-negative numbers. Providing a negative number will result in an error.
  • Fractional numbers are truncated to integers before the function is applied.
  • The double factorial grows at a slower rate compared to a standard factorial but still can become very large quickly for larger inputs. Ensure your results do not exceed Excel's numeric limits.
  • Double factorials are often used in combinatorics, physics, and mathematical problems involving specific types of series or sequences.

Tip: The FACTDOUBLE function is useful when working with problems involving alternate terms in factorial series, and it can simplify calculations involving only odd or even terms!