APP description

Double-order multiplier represents"m!!" . When m is a natural number, it represents the product of all positive integers that do not exceed m and have the same parity as m.

Example：

3!!=1*3=3

5!!=135=15

6!!=246=48

8!!=246*8=384

Another 0!!=1!!=1

Usage example

Enter the value:

Number: 9

Click "Calculate" to output the value.

Double factorial: 945

Note

The double factorials of the first 6 positive integers are: 1!!=1, 2!!=2, 3!!=3, 4!!=8, 5!!=15 and 6!!=48.