English Explanatory Dictionary

double factorial

English dictionary entry

Meanings

noun
  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.

Word forms

double factorial double factorials

Etymology

From double + factorial.

Synonyms

semifactorial
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