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I can prove that for any positive $\mathbb{Z+}$ the conjecture will always converge to 4 hence entering the loop. $$ 4 \to 2 \to 1 \to 4 \to ... $$ To do this I used the formula of odd number and even number as follows: $$odd = 2x + 1$$ $$even = 2x$$ The rule says: $$odd \to 3x + 1$$ $$even \to \...