Geometrically growing pmf

Let $X$ be a random variable such that $P(X = i) = 2P(X = i - 1)$, $i = 2, 3, \dots, n$, $n \ge 7$, and $\sum_{i=1}^{n} P(X = i) = 1$. Then $(2^n - 1)P(X = 7)$ equals ________ (answer in integer).