A number game

Take any positive whole number. Call it x.

If x is even, divide it by two. If x is odd, triple it and add 1.

Your result is the new value of x. Repeat the steps above.

Keep doing it.

This process appears to always reach the number 1. But nobody has ever been able to prove that it always tends to 1. Nor has anyone every found an exception (a counterexample)

This is known as the Collatz conjecture, and it dates to the year 1937.

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example: start with 22


22
11
34
17
52
26
13
40
20
10
5
16
8
4
2
1