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1992 AMC 12 Question 15

AMC12 · 1992 AMC 12

Question 15

Let $i=\sqrt{-1}.$ For $n\ge1,$ define a sequence of complex numbers by $$
\begin{aligned} z_1&=0,\\ z_{n+1}&=z_n^2+i. \end{aligned}
$$ In the complex plane, how far from the origin is $z_{111}?$
  1. $1$
  2. $\sqrt2$
  3. $\sqrt3$
  4. $\sqrt{110}$
  5. $\sqrt{2^{55}}$