Calculate the multifactorial 9!!
We have 2 exclamation symbols (!)
Start at 9
Iterate backwards in steps of 2
Stop when we hit 1 or below
Term 1
For term 1, we start with 9
Term 2
Subtract -1 x 2 = -2 to get n(n - -2)
(n - -2) → 9 - -2 = 7
Our factorial term is:
9(7)
Term 3
Subtract -1 x 2 = -2 to get n(n - -2)(n - -2)
(n - -2) → 9 - -2 = 5
Our factorial term is:
9(7)(5)
Term 4
Subtract -1 x 2 = -2 to get n(n - -2)(n - -2)(n - -2)
(n - -2) → 9 - -2 = 3
Our factorial term is:
9(7)(5)(3)
Term 5
Subtract -1 x 2 = -2 to get n(n - -2)(n - -2)(n - -2)(n - -2)
(n - -2) → 9 - -2 = 1
Our factorial term is:
9(7)(5)(3)(1)
Build final multifactorial:
9!! = n(n - -2)(n - -2)(n - -2)(n - -2)...
9!! = 9(7)(5)(3)(1)
Final Answer
9!! = 945
