Sunday, 16 April 2017

divisibility - Prove that for every natural $n$, $(n^2 + n)(n^2 + 2)$ can be divided by $6$



Prove that for every natural number $n$, $(n^2 + n)(n^2 + 2)$ can be divided by $6$.




I've noticed that $(n^2 + n) = n(n+1)$ so these are two successive numbers hence one of them can be divided by two.



I suppose that I should prove that $(n^2 + n)(n^2 + 2)$ can be divided by $3$ but I don't know how to do that.


Answer



Either $n$ is divisible by $3$, or $n^2+2=(n+1)(n-1)+3$ is.


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