Let $a_1= 2$, and for each $y > 1$, define $a_{y+1} = a_y(a_y −1) +1$.
Prove that for all $x \ne y$, $a_x$ and $a_y$ are coprime.
Let $a_1= 2$, and for each $y > 1$, define $a_{y+1} = a_y(a_y −1) +1$.
Prove that for all $x \ne y$, $a_x$ and $a_y$ are coprime.