1+x+x^2+....x^{n-1} is a prime....
Prove 'n' is a prime.
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7 Answers
62Is this a doubt or a question you have posted for others...
* does it really need to go in the section Olympiad stuff?
11BTw....I just got the soln within 1 minute after giving this qsn...lol!
No need for soln pls!
Really silly of me!
62lol.. okie.. lets leave this one for the class IX - X guys ;) ??
1adding we get sum= \frac{1(x^n-1)}{x-1}
let n be a composite no, we have n=ab for some a,b≠1
now \frac{(x^a)^b-1^b}{x-1} is always an integer as a^n-b^n is always divisible by a-b
hence if n is composite, sum is composite → if n is prime sum is prime