Maths Olympiad Prep

Library / /142 of 520

Number theory Difficulty 5.8 AIME, harder Find the answer

33. Let nn be a positive integer. We define
T(n)={n/2 if n is even (3n+1)/2 if n is odd T(n)=\left\{\begin{array}{ll} n / 2 & \text { if } n \text { is even } \\ (3 n+1) / 2 & \text { if } n \text { is odd } \end{array}\right.

We then form the sequence obtained by iterating TT; n,T(n),T(T(n)),T(T(T(n))),n, T(n), T(T(n)), T(T(T(n))), \ldots. For instance, starting with n=7n=7 we have 7,11,17,26,13,20,10,5,8,4,2,1,2,1,2,17,11,17,26,13,20,10,5,8,4,2,1,2,1,2,1 \ldots. A well-known conjecture, sometimes called the Collatz conjecture, asserts that the sequence obtained by iterating TT always reaches the integer 1 no matter which positive integer nn begins the sequence.
a) Find the sequence obtained by iterating TT starting with n=29n=29.
b) Show that the sequence obtained by iterating TT starting with n=(2k1)/3n=\left(2^{k}-1\right) / 3, where kk is an even positive integer, k>1k>1, always reaches the integer 1 .

A number or a short expression. Spacing and $ signs are ignored.

Solutions — 2

Solution 1

None

Solution 2

None

Translate the text above into English, please retain the original text's line breaks and format, and output the translation result directly.

Note: The provided instruction is a meta-instruction and not part of the text to be translated. Since the text to be translated is "None", the translation is also "None". Here is the formatted output as requested:

None

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.