Prime or not? | n^4-22n^2+9

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[umdorumdor]

on mod 3 will be n^4 - n^2 = n^2*(n-1)*(n+1) = 0 always, means, it is not prime

[yoav]

very nice!! i solved it by n^2(n^2-22)+9 so if n=0 mod3 this number dibided by 3, and if n=1, 2 mod 3 than n^2-22=0 mod3 so this number also divided by 3.since this number dose not equal to 3, it can never be prime. 💯