Standard +0.3 This is a straightforward proof by induction with a divisibility statement. The base case is trivial (n=1 gives 4+45=49), and the inductive step requires standard algebraic manipulation to factor out 7 from 2^{k+2} + 5×9^{k+1} using the inductive hypothesis. While it requires careful algebra, it follows a well-practiced template with no novel insight needed, making it slightly easier than average.