Răspuns :
[tex]3^n=numar\ impar\ \forall n\in N^* \\ 1^n=numar\ impar\ \forall n\in N^* \\ 3^n+1^n=numar\ par\ \forall n\in N^* \\ 3^n+1^n+2^n=numar\ par\ \forall n\in N^* \\ \rightarrow2|1^n+2^n+3^n\ \forall n \in N^*[/tex]