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MathNet 2016-part-07 — 182 problems (EN–VI) Question 21

Math Olympiad Vault · MathNet 2016-part-07 — 182 problems (EN–VI)

Question 21

The distinct prime factors of an integer are its prime factors listed without repetition. For example, the distinct prime factors of $40$ are $2$ and $5$.

Let $A = 2^{k} - 2$ and $B = 2^{k} \cdot A$, where $k$ is an integer $(k \gt 1)$.

Show that, for every choice of $k$,

a. $A$ and $B$ have the same set of distinct prime factors.

b. $A+1$ and $B+1$ have the same set of distinct prime factors.