# Elementary Number Theory Problems 4.2 Solution (David M. Burton's 7th Edition) - Q16

My Solution for "Use the theory of congruences to verify that $$89 \mid 2^{44} - 1 \qquad \text{and} \qquad 97 \mid 2 ^{48} - 1$$"

Background

All theorems, corollaries, and definitions listed in the book's order:

**I will only use theorems or facts that are proved before this question**. So, you will not see that I quote theorems or facts from the later chapters.

## Question

Use the theory of congruences to verify that $$89 \mid 2^{44} - 1 \qquad \text{and} \qquad 97 \mid 2 ^{48} - 1$$

## Solution

For $89 \mid 2^{44} - 1$:

$$ \begin{equation} \begin{split} 2^{44} - 1 & \equiv (2^{11})^{4} - 1 \\ & \equiv 2048^{4} - 1 \\ & \equiv 1^{4} - 1 \\ & \equiv 0 \pmod {89} \end{split} \nonumber \end{equation} $$So, $89 \mid 2^{44} - 1$.

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