1. The problem statement, all variables and given/known data Prove that 7^n - 1 is divisible by 6 2. Relevant equations 3. The attempt at a solution I managed a solution were i use only the addition of 6^x were x is any postive integer. The solution i have workes until n = 3 but not after that. 7^n - 1 = 6^n + n*6^(n-1) + n*6^(n-2)...... 7^1 - 1 = 6 = 6^1 7^2 - 1 = 48 = 6^2 + 2*6^1 7^3 - 1 = 342 = 6^3 + 3*6^2 + 3*6^1 I tried different other possibilities on this. I also thought about rewriting 7^n - 1 such that division by six is obvious but i couldn't think of a possibility. I'm guessing i need a totally different approach bu i don't know what approach. Anyone got a clue on were to look? Proving has to go by mathematical induction but that for later.