Main Index Number Theory Sequences Recurrent sequences Linear recurrent sequences First order sequences Factorial numbers
  Subject Index
comment on the page

Double factorial

The double factorial typeset structure of a non-negative integer typeset structure is defined as the product of all integers less or equal to typeset structure that have the same parity, that is

n !! = {1, if n = 0 or 1, n · ((n - 2) !!), if n > 1 .(1)

We have

(2 n) !! = 2^n n !(2)

and

(2 n + 1) !! = (2 n + 1) !/(2^n n !) .(3)

To compute some values of the double factorial function go to .

Cite this web-page as:

Štefan Porubský: Double factorial.


Page created   .