2009 AMC 12A Problem 24


The ‘‘tower function of twos’’ is defined recursively as follows: T(1)=2T(1) = 2 and T(n+1)=2T(n)T(n + 1) = 2^{T(n)} for n1n\ge1. Let A=(T(2009))T(2009)A = (T(2009))^{T(2009)} and B=(T(2009))AB = (T(2009))^A. What is the largest integer kk such that

log2log2log2log2Bk\log_2\log_2\log_2\ldots\log_2B_{k}where there are kk log2\log_2's, is defined?

(A) 2009(B) 2010(C) 2011(D) 2012(E) 2013\textbf{(A)}\ 2009\qquad \textbf{(B)}\ 2010\qquad \textbf{(C)}\ 2011\qquad \textbf{(D)}\ 2012\qquad \textbf{(E)}\ 2013


Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.

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Category: AMC 12A
Points: 5
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