FACTDOUBLE in Collabora Office: Calculate Even and Odd Factorial Products

• Introduced: original Collabora release and launch date are not established by the sources reviewed.
• Availability: documented in Collabora Office 26.04 help, scoped to the desktop-help release.
• Platform scope: support in every online or mobile deployment is not inferred from desktop documentation.
• Checked: October 14, 2026. Function-specific documentation and independently derived controls; no native Collabora test was performed.

=FACTDOUBLE(number)

The official Collabora reference specifies an integer greater than or equal to zero. Even arguments use the even factors; odd arguments use the odd factors. It explicitly defines FACTDOUBLE(0) as 1.

The notation n!! means double factorial. It does not mean (n!)!, and it does not mean 2*n!. Use English function names; multiargument helper formulas here use semicolon separators.

=FACTDOUBLE(8)
=FACTDOUBLE(7)
=FACTDOUBLE(0)

Expected results: 384, 105 and 1. The first two expansions are 8×6×4×2 and 7×5×3×1. The zero result is a defined empty-product convention rather than a multiplication by zero.

For another explicit small control, FACTDOUBLE(1) is 1 and FACTDOUBLE(2) is 2. Those values anchor the two separate even and odd sequences.

Enter integers 0 through 8 in A2:A10. In B2 enter =FACTDOUBLE(A2) and fill down.

Each value from argument two onward equals its argument times the result two rows earlier in this argument sequence. Adjacent entries do not follow the ordinary factorial recurrence because the factors alternate parity.

For n=8, compare:

=FACTDOUBLE(8)
=8*FACTDOUBLE(6)

Both expected results are 384. For n=7, the corresponding expression =7*FACTDOUBLE(5) gives 105.

Do not apply this recurrence blindly to n=0 or n=1 by creating negative arguments. Their base values are handled directly. The documented domain here does not authorize extending negative double-factorial conventions from mathematical texts into Calc.

For eight distinct objects, the number of ways to split all objects into four unordered pairs is 7×5×3×1. The first object has seven possible partners, the first remaining object then has five, and so on.

=FACTDOUBLE(7)

Expected pairing count: 105. A separate check is:

=FACT(8)/(2^4*FACT(4))

This also gives 105. The factors in the denominator remove order within each pair and order among the four pairs. The model assumes all objects are distinct and every pairing is permitted.

For six distinct objects the corresponding count is FACTDOUBLE(5), or 15. Restrictions on which objects may be paired require another model; FACTDOUBLE does not know those restrictions.

For nonnegative integer k, the mathematical identity is (2k)!! = 2^k*k!. With k=4:

=2^4*FACT(4)

Expected result: 384, matching FACTDOUBLE(8). FACT multiplies every positive integer up to its input; FACTDOUBLE selects one parity sequence.

Check that the argument is an allowed whole number and that double factorial is the intended operation. FACT(8) is 40320, considerably larger than FACTDOUBLE(8), despite the similar names.

The direct help specifies the nonnegative-integer domain but does not supply the complete native error, fractional-input or maximum-exact-integer policy. These small counts were independently checked; they do not establish that arbitrarily large products remain exact or finite in the application.

• Collabora Office 26.04: FACTDOUBLE.
• Editorial testing standards.

The direct product reference establishes the function definition and syntax. Worked examples were independently calculated; no native Collabora execution or broader client certification is claimed.