1. The problem statement, all variables and given/known data Prove by induction, that when r(r-1)(r+1) is an even integer when r=2,3,4.... 2. Relevant equations Prove by induction 3. The attempt at a solution I began with the base case r=2, leading 6. Then I proceed with r=3, leading 24. Now if r=k is true, then k(k-1)(k+1) is also true. If r=k+1, then (k+1)(k)(k+2) But now I'm stuck at this point - how do I proceed with this?