# Problem 44448. Project Euler: Problem 14 Longest Collatz sequence

This problem is a hard version of "Problem 42673. Longest Collatz Sequence", because of time limits. https://ww2.mathworks.cn/matlabcentral/cody/problems/42673-longest-collatz-sequence

The following iterative sequence is defined for the set of positive integers:

n → n/2 (n is even) n → 3n + 1 (n is odd)

Using the rule above and starting with 13, we generate the following sequence:

13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1 It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1.

Which starting number, no more than N, produces the longest chain, and how long? Don't cheat!

### Solution Stats

5.34% Correct | 94.66% Incorrect
Last Solution submitted on Feb 26, 2024

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