23n−7n−1 is divisible by

Let P(n)=23n−7n−1P(1)=0, P(2)=49P(1) and P(2) are divisible by 49.P(k)≡23k−7k−1=49m∴P(k+1)≡23k+3−7k−8=8(49m+7k+1)−7k−8=49(8m)+49k=49pHence, by mathematical induction 23n−7n−1 isdivisible by 49.