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Find the sum of all prime numbers such that can be represented as where is an integer.
The answer is 7.
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1 solution
a^3-1=(a-1)(a^2+a+1), because a^3-1 is prime number so a^3-1= (1)(p). exactly a^2+a+1 is impossible to be 1. the consequence is a-1=1. a=2.
a^3-1=2^3-1=7