Alternatives to say "顾名思义＂ I am reading a book to explain factorial. 

n! = n*(n-1)*(n-2)....3*2*1 


Decompose word factorial阶乘, I am enlightened to see its meaning literally.

Since Factor is 乘数, So factorial should 阶乘.

How to describe such a situation? 

"顾名思义"? 从字面上理解? 从拼写上理解?    

I assume 顾明思议 a bit better but merely not grasp the idea thoroughly.

Are there some better phases?
What I can think of is: 逐字理解 or 按字面意思理解.