Methods of Proof
There have been many methods of attack on the problem. For example, let A and B be integers, A being how many times the "3n+1" rule is used in a cycle, and B being how many times the "n/2" rule is used. Let x be the lowest number in a cycle then, regardless of what order the rules are used, we have:
where C is the "excess" caused by the "+1" in the rule, and can be shown to be bigger than:
using geometric progression. Rearranging shows that the lowest number in the cycle satisfies:
which gives a lower bound for the lowest number in a cycle for a given cycle length. For large cycles the fraction 3A/2B would be expected to tend to 1, so that the lower bound would be large.
Read more about this topic: Collatz Conjecture
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