Odd Factorial Sum Digit
The double factorial, denoted by $ n!\phantom{}!$, returns the product of all of the odd integers that are less than or equal to $ n $. For example, $ 7!\phantom{}!= 7 \times 5 \times 3 \times 1 $. What is the units digit of $ 1!\phantom{}!+ 3!\phantom{}!+ 5!\phantom{}!+ 7!\phantom{}!+ \cdots + 49!\phantom{}!$?
- 1
- 2
- 3
- +
- 4
- 5
- 6
- -
- 7
- 8
- 9
- $\frac{a}{b}$
- .
- 0
- =
- %
- $a^n$
- $a^{\circ}$
- $a_n$
- $\sqrt{}$
- $\sqrt[n]{}$
- $\pi$
- $\ln{}$
- $\log$
- $\theta$
- $\sin{}$
- $\cos{}$
- $\tan{}$
- $($
- $)$
- $[$
- $]$
- $\cap$
- $\cup$
- $,$
- $\infty$