Chapter 5.5, Problem 5ES

Exercise 1-5 conrain a while loop and a predicate. In each case show that if the predicated is true before entry to the loop, then it is also after exit from the loop.
$\begin{array}{c}\text{loop:}\text{while }\left(n\ge 3\text{and}n\le 100\right)\\ n:=n+1\\ \text{end}\text{while}\end{array}$

Predicate: $2n+1\le 2^n$