Phrase guide

double factorial

noun · 1 senses · updated from the 2026-07-25 local source snapshot

Definitions and examples are grouped by meaning. Pronunciation, history, word forms, translations, descendants, synonyms, antonyms, derived terms, and related words appear whenever the source provides them.

Sound

Pronunciation

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1

noun

Meaning 1

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.

Definition source: English Wiktionary via Wiktextract

Topics: combinatorics, mathematics, sciences

No example sentence was provided for this meaning.

Meaning relationships

Synonyms: semifactorial

Antonyms: none provided

History

Etymology

From double + factorial.

Across languages

Translations

9 source translations are retained for this English entry.

  • Catalan: doble factorial — mathematics
  • Dutch: dubbelfaculteit — mathematics
  • Esperanto: duopa faktorialo — mathematics
  • French: double factorielle — mathematics
  • German: Doppelfakultät — mathematics
  • German: doppelte Fakultät — mathematics
  • Portuguese: duplo fatorial — mathematics
  • Spanish: doble factorial — mathematics
  • Thai: ดับเบิลแฟกทอเรียล — mathematics