Returns the double factorial of a number. Double factorial (n!!) multiplies every other number: for even n, n!! = n × (n-2) × ... × 4 × 2; for odd n, n!! = n × (n-2) × ... × 3 × 1. Essential for advanced combinatorics, probability theory, and mathematical analysis.
Master the fundamentals of Excel FACTDOUBLE function
The FACTDOUBLE function returns the double factorial of a number. Double factorial (n!!) is defined differently for even and odd numbers: For even n: n!! = n × (n-2) × (n-4) × ... × 4 × 2. For odd n: n!! = n × (n-2) × (n-4) × ... × 3 × 1. Special cases: 0!! = 1, (-1)!! = 1. Double factorial grows slower than regular factorial but still rapidly. Essential for advanced combinatorics, probability theory, integrals involving trigonometric functions, and mathematical analysis.
Different formulas for even/odd
0!! = 1, (-1)!! = 1
Grows slower than FACT
Must be ≥ -1
Function-specific parameters
Function-specific return type
Double factorial in combinatorics
Probability calculations
Integrals and series
Mathematical special functions
Exact matching required
Returns numeric position
Handles missing text gracefully
=FACTDOUBLE(number)The value for which you want to calculate the double factorial. Must be greater than or equal to -1.
The double factorial of the number
Description: Returns the double factorial of a number
Double factorial of even number
Returns 48 because 6!! = 6 × 4 × 2 = 48. For even n, multiply every other even number.
Use FACTDOUBLE function in VBA
' Basic FACTDOUBLE in VBA
Range("C1").Value = Application.WorksheetFunction.FactDouble(6)
' Returns: 48
' Calculate double factorial
Sub CalculateFACTDOUBLE()
Dim number As Integer
number = Range("A1").Value
Dim result As Double
result = Application.WorksheetFunction.FactDouble(number)
Range("B1").Value = result
End Sub
' Calculate for both even and odd
Sub CalculateEvenOddFACTDOUBLE()
Dim evenNum As Integer
Dim oddNum As Integer
evenNum = Range("A1").Value
oddNum = Range("A2").Value
Dim evenResult As Double
Dim oddResult As Double
evenResult = Application.WorksheetFunction.FactDouble(evenNum)
oddResult = Application.WorksheetFunction.FactDouble(oddNum)
Range("B1").Value = evenResult
Range("B2").Value = oddResult
End Sub
' Generate double factorial table
Sub GenerateFACTDOUBLETable()
Dim i As Integer
For i = 0 To 10
Dim factDoubleValue As Double
factDoubleValue = Application.WorksheetFunction.FactDouble(i)
Range("A" & (i + 1)).Value = i
Range("B" & (i + 1)).Value = factDoubleValue
Next i
End Sub
' Compare with regular factorial
Sub CompareFACTFACTDOUBLE()
Dim number As Integer
number = Range("A1").Value
Dim factValue As Double
Dim factDoubleValue As Double
factValue = Application.WorksheetFunction.Fact(number)
factDoubleValue = Application.WorksheetFunction.FactDouble(number)
Range("B1").Value = factValue
Range("B2").Value = factDoubleValue
Range("B3").Value = factValue / factDoubleValue
End SubDouble factorial in combinatorics
Probability calculations
Integrals and series
Mathematical special functions
FACTDOUBLE returns #NUM! for numbers < -1
=IF(A1>=-1, FACTDOUBLE(A1), "Invalid")Solution: FACTDOUBLE only works with numbers ≥ -1. FACTDOUBLE(-2) and smaller return #NUM!. Ensure input is ≥ -1. Special case: FACTDOUBLE(-1) = 1.
Non-numeric input in FACTDOUBLE
=FACTDOUBLE(VALUE(A1))Solution: Ensure input is numeric. FACTDOUBLE requires a number. Check for text, errors, or empty cells. Use VALUE() if needed.
Mixing FACTDOUBLE with FACT
FACTDOUBLE(6) = 48, FACT(6) = 720Solution: FACTDOUBLE (n!!) is different from FACT (n!). FACTDOUBLE multiplies every other number, FACT multiplies all numbers. FACTDOUBLE grows slower than FACT.
Uncertainty about even vs odd behavior
6!! = 6×4×2, 7!! = 7×5×3×1Solution: Even n: multiply every other even number (n, n-2, ..., 4, 2). Odd n: multiply every other odd number (n, n-2, ..., 3, 1).