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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.

  • 0
    In the second equality of the first line, in the left side, it must be $\,a_{y+1}\,$ , I think...and not what you wrote.2012-12-10
  • 0
    Yes, you're right. Thank you.2012-12-10
  • 1
    You have to enclose the $y+1$ in curly braces to make it a subscript: `a_{y+1}`.2012-12-10

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