The words used just once or more than once are in verses that have a meaning. Understand the meaning and you may learn something.
Counting words is good for learning to count, but that was not the intention of the Author of the Quran.
4:140 He has already revealed to you in the Book that, when you hear the revelations of God being rejected and ridiculed, sit not with them unless they engage in some other conversation. Otherwise you will bear similar guilt as they bear. God will gather hypocrites and rejecters together, all of them, into Hell. [4:63, 6:68]