Difference between factorial and double factorial
The double factorial of a number n, denoted by n‼, is the product of all positive integers up to n that have the same parity (odd or even) as n.
The double factorial of 4, denoted as 4!!, is calculated by multiplying all positive integers up to 4 that share the same parity as 4. For even numbers like 4, the double factorial involves multiplying all even integers up to 4. Therefore, 4!! = 4 × 2 = 8. This calculation follows the general rule for double factorials where the product includes numbers of the same parity as the given number. In this case, 4!! results in 8.
For the double factorial of 3, the process is similar. Since 3 is an odd number, the double factorial involves multiplying all odd integers up to 3. Thus, 3!! = 3 × 1 = 3.
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