Find a prime factor of A=147+142+1. Obviously without just computing it.
Answer
Hint: I've seen the 3rd cyclotomic polynomial too many times.
x7+x2+1=(x7−x4)+(x4+x2+1)=x4(x3−1)+x6−1x2−1=x4(x+1)(x2+x+1)+(x3−1)(x3+1)(x−1)(x+1)=x4(x+1)(x2+x+1)+(x2+x+1)(x2−x+1)
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