FACTDOUBLE Function in ONLYOFFICE Spreadsheet Editor: Double Factorials and Worked Examples

• Introduced: The original introduction version and date are not established by the official sources checked.
• Availability: Documented in the current ONLYOFFICE Spreadsheet Editor help; no final working-version endpoint is established.
• Scope: Docs and Desktop Editors release separately. This unversioned help does not establish availability in every older build, mobile client or deployment.
• Checked: October 14, 2026, against the official function reference. Documentation check; not a new native test.

For a nonnegative integer n, the mathematical double factorial is the product of the integers with the same parity as n, stepping down by two. For example, 7!! = 7 × 5 × 3 × 1 = 105, whereas 8!! = 8 × 6 × 4 × 2 = 384. By mathematical convention, 0!! = 1 and 1!! = 1. These are mathematical definitions: the reference does not explicitly spell out what the editor returns for zero or for unusual numeric values; check such boundary cells natively before relying on them in a critical workbook.

Double factorials appear in probability formulas, products involving odd or even sequences, series expansions and checks on certain combinatorial identities. The two exclamation marks here are mathematical notation, not formula punctuation: type FACTDOUBLE(...), not n!!, inside an editor formula.

=FACTDOUBLE(number)

There are no optional arguments and no documented default. The current official page places FACTDOUBLE under Math and Trigonometry and names its sole argument number. For reproducibility all sample inputs below are nonnegative whole numbers; that is a safe mathematical teaching domain, not an assertion that the editor rejects all other inputs. Function definition (checked 2026-10-13 UTC).

1. Open a new, disposable worksheet. Enter Input n into A1, Formula into B1, and Mathematical expectation into C1.
2. Enter the integers 0 through 12 into A2:A14, one per row. Do not enter 0!! with punctuation in column A.
3. In B2 enter =FACTDOUBLE(A2) and press Enter. For each subsequent row, enter the matching formula shown below or fill down B2 through B14.
4. Record the observed result in a separate column if you actually run the editor; compare it to the independently computed C-column expected value. Do not paste an expected value into B and claim it came from ONLYOFFICE.

Worked example: B7 corresponds to A7=5, so =FACTDOUBLE(A7) has the mathematical expectation 5 × 3 × 1 = 15. B10 uses A10=8 and expects 384. This table was calculated in Python using integer multiplication with a decrement of two, not evaluated in ONLYOFFICE.

For any whole number m ≥ 0, the identity (2m)!! = 2^m × m! holds mathematically. Put 4 in A2 and compare these formulas on an experimental sheet:

=FACTDOUBLE(2*A2)
=POWER(2,A2)*FACT(A2)

Both expressions have expected value 384 (8!! = 384 and 2^4 × 4! = 16 × 24). This also checks whether an editor handles nested functions consistently. The official POWER and FACT references document the names, but no nested calculation was executed in the native editor during research.

For positive integers m, the odd double-factorial identity is (2m−1)!! = (2m)! / (2^m × m!). Enter 5 in A3 and independently compare:

=FACTDOUBLE(2*A3-1)
=FACT(2*A3)/(POWER(2,A3)*FACT(A3))

Both have expected value 945: 9 × 7 × 5 × 3 × 1 = 945, also 10! ÷ (32 × 5!) = 945. If testing large m, be aware that the quotient representation may round differently from a direct product even when both are mathematically equal.

• FACT versus FACTDOUBLE: =FACT(6) is mathematically 720, but =FACTDOUBLE(6) is 48. One multiplies every positive integer; the other every second integer. Related official FACT reference.
• Even versus odd n: 7!!=105 while 8!!=384. The parity dictates which factors occur; a double factorial is not (n!)! and not (n!)×2.
• Zero and one: 0!! and 1!! are both 1 in mathematics. Whether specific ONLYOFFICE versions accept these boundary cases exactly must be recorded through native tests.
• Negative, fractional, text and excessively large inputs: the short official FACTDOUBLE reference does not list precise treatment, truncation or native error strings. Avoid inventing an Excel-compatible error code. Test and record the actual editor result; do not extrapolate from this article.

FACT calculates ordinary factorials; POWER provides powers of two used in the identities; COMBIN and PERMUT are different counting functions, not aliases for FACTDOUBLE. Each hyperlink points to official ONLYOFFICE documentation.

The exact function name, category, syntax and numeric argument are documented directly in the official FACTDOUBLE page checked 2026-10-13 UTC. The recurrence, double-factorial table and identities above were calculated independently and are not additional vendor implementation promises. Open native verification questions: FACTDOUBLE(0), FACTDOUBLE(-1), FACTDOUBLE(3.2), FACTDOUBLE("5"), overflow/precision and same-formula results in Docs web versus Desktop at known versions.

ONLYOFFICE’s official inserting-functions instructions say to select a cell, type =, enter a recognized function and comma-separated arguments in parentheses, then press Enter; alternatively open the Formula tab, choose Function, search for the name, and fill the argument dialog. The formulas above are written with English function names and comma separators following the published help examples. If your workbook uses a different Formula Language, confirm the localized name in the Function dialog rather than manually translating an English name. This manuscript does not claim that any additional separator style was executed.

Regional settings and formula language

The official Advanced Settings page explains File → Advanced Settings → Regional settings. Formula Language determines translated formula and argument labels. Region influences displayed currency, dates, and times. Separate decimal and thousands separators are customizable. These documented settings are not evidence that a given translated function, localized punctuation style, or imported workbook behaves identically in every deployment. All tables here use ordinary integer inputs so decimal-entry ambiguity is avoided; they have not undergone native non-English testing.

Calculation and validation limits

The listed results are independently calculated mathematical expectations, not observed outputs from a running ONLYOFFICE Desktop, Docs/web, or self-hosted editor. We performed the arithmetic using Python’s integer mathematics; the result checks do not establish formula-parser or spreadsheet-engine support. Enter these test cases on a disposable sheet and compare the editor’s displayed result with the expectation. If different, record the precise ONLYOFFICE version, environment (web/Desktop), formula language, cell type, and exact displayed error before drawing a conclusion about compatibility.

Do not infer first-supported release or universal compatibility. The unversioned help function reference lists this function today, but does not identify the first supported Desktop build or prove behaviour across all self-hosted, Docs/web and embedded editions. The Docs changelog lists Docs 10.0.0, 2026-10-10, while the Desktop Editors changelog is maintained separately; the Docs release alone is not a Desktop version guarantee. No platform-specific native tests or compatibility matrix were executed for this page.

1. Formula displayed as text: ensure the cell contains a formula beginning with =, not a quoted string; check the displayed cell format.
2. Unexpected result: verify the order of arguments, positive/nonnegative integer assumption used in the examples, input cells (not headers), and number formatting. Compare with the arithmetic shown rather than a screenshot.
3. Function not recognized: search in the editor’s Insert Function dialog, check Formula Language, and note the exact desktop/web version. Presence in current web documentation does not guarantee the function was present in older releases.
4. Apparent calculation error: check blank cells, stray text, missing commas, copied relative references and whether the input violates the mathematical domain. The help reference does not provide a comprehensive table of exact error strings for this function; no error code or coercion behaviour is asserted here as an observed ONLYOFFICE result.
5. Large numbers: factorial-style counts can exceed the range where a spreadsheet displays or stores every integer exactly. A rounded display or scientific notation is not proof that the full integer was retained; compare against the independently calculated exact integer where precision matters.

• Official function-entry instructions — how to insert and identify the supported function from the editor UI.
• Official regional and formula-language settings — language, region and separator controls; localized formula execution remains untested.
• ONLYOFFICE Docs release notes and Desktop release notes — separate release tracks; these do not establish this function’s introduction version.

Verification limitations: Native web/Desktop calculation, localized parsing, historical compatibility and undocumented error behavior were not tested. The official function index documents current names, not a release-by-release execution guarantee.