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2019 AMC 12B Question 22

AMC12 · 2019 AMC 12B

Question 22

Define a sequence recursively by $x_0=5$ and

$$
x_{n+1}=\dfrac{x_n^2+5x_n+4}{x_n+6}
$$

for all nonnegative integers $n.$ Let $m$ be the least positive integer such that

$$
x_m\le4+\dfrac{1}{2^{20}}.
$$

In which of the following intervals does $m$ lie?
  1. $[9,26]$
  2. $[27,80]$
  3. $[81,242]$
  4. $[243,728]$
  5. $[729,\infty)$