# Math Help - Arithmetic proof

1. ## Arithmetic proof

Prove that, for all n, n^3 + 2n^2 - n - 1 is not divisible by 3.

I hate to ask a question like this...but how do I get started here? I don't even know where to start. Could anyone just tell me the first starting steps in order to prove this and/or the concept that would prove this true? Any help would be appreciated.

2. Originally Posted by SterlingM
Prove that, for all n, n^3 + 2n^2 - n - 1 is not divisible by 3.

I hate to ask a question like this...but how do I get started here? I don't even know where to start. Could anyone just tell me the first starting steps in order to prove this and/or the concept that would prove this true? Any help would be appreciated.
You need only check it for the cases $n=0,1,2$ where you get $-1,1,13$ respectively.