double factorial

double factorial noun: for an odd integer, the result of multiplying all the odd integers from 1 to the given number; or for an even integer, the result of multiplying all the even integers from 2 to the given number; symbolised by a double exclamation mark (!!). For example, 9!! = 1 × 3 × 5 × 7 × 9 = 945.

Noun

double factorial (plural double factorials)

For an odd integer, the result of multiplying all the odd integers from 1 to the given number; or for an even integer, the result of multiplying all the even integers from 2 to the given number; symbolised by a double exclamation mark (!!). For example, 9!! = 1 × 3 × 5 × 7 × 9 = 945.
- The symbolical representation of the results of this paper is much facilitated by the introduction of a separate symbol for the product of alternate factors, n#92;cdotn-2#92;cdotn-4#92;cdots 1, if n be odd, or n#92;cdotn-2#92;cdots 2 if n be odd^([sic – meaning even]). I propose to write n#33;#33...1902, Arthur Schuster, “On some Definite Integrals and a New Method of reducing a Function of Spherical Co-ordinates to a Series of Spherical Harmonics”, in Proceedings of the Royal Society of...
- The double factorial notation #92;begin#123;align#125;(2n)#33;#33;amp;#61;2#92;cdot 4#92;cdot 6#92;cdots(2n-2)(2n)#61;2#123;n#125;n#33;#92;#92;(2n#43;1)#33;#33;amp;#61;1#92;cdot 3#92;cdot...1948 September, B. E. Meserve, “Double Factorials”, in The American Mathematical Monthly, volume 55, number 7, →DOI, →JSTOR, page 425
Synonyms:

semifactorial

double factorial meaning in Thai

double factorial in Thai

mathematics: ดับเบิลแฟกทอเรียล

Examples of double factorial in a sentence

The symbol #33;#33; in Eq. (9) denotes the double factorial given by n#33;#33;#61;n(n-2)(n-4)#92;dots#92;kappa#95;n, where #92;kappa#95;n is 1 for odd n and 2 for even n.2008 April, Adriana Pálffy, Jörg Evers, Christoph H. Keitel, “Electric-dipole-forbidden nuclear transitions driven by super-intense laser...
Double factorials can also be defined recursively.2012 June, Henry Gould, Jocelyn Quaintance, “Double Fun with Double Factorials”, in Mathematics Magazine, volume 85, number 3, →DOI, pages...

Synonyms of double factorial

semifactorial

Forms of double factorial

plural	double factorials

Origin of double factorial

From double + factorial.

Questions about double factorial

What does double factorial mean?: Double factorial means for an odd integer, the result of multiplying all the odd integers from 1 to the given number; or for an even integer, the result of multiplying all the even integers from 2 to the given number; symbolised by a double exclamation mark (!!). For example, 9!! = 1 × 3 × 5 × 7 × 9 = 945.
What is double factorial in Thai?: Double factorial in Thai is ดับเบิลแฟกทอเรียล. See Double factorial meaning in Thai.
How do you use double factorial in a sentence?: The symbol #33;#33; in Eq. (9) denotes the double factorial given by n#33;#33;#61;n(n-2)(n-4)#92;dots#92;kappa#95;n, where #92;kappa#95;n is 1 for odd n and 2 for even n.
What part of speech is double factorial?: Double factorial is a noun.
What is the plural of double factorial?: The plural of double factorial is double factorials.

Words near double factorial in the dictionary

Adapted from Wiktionary: double factorial (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

Last updated: 2026-09-02

Cite this entry: “double factorial.” Word.ws, https://word.ws/double_factorial. Based on Wiktionary, CC BY-SA 4.0.