# Math Help - Divisibility 7

1. ## Divisibility 7

Show that: $a,b\in \mathbf{Z^{+}}$ and $b>2 \Rightarrow 2^{a}+1\nmid2^{b}-1$

2. What about: $a = 3, \ b = 6$

$2^3 + 1 = 9 \mid 63 = 2^6 - 1$