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Recently our lecturer told us that it is an unsolved mathematical problem if the following while loop aka iteration ever terminates. Unfortunately I forgot to ask him what it is called. If someone recognizes this "problem" I would be glad to know what it is called.

Let $n$ be a natural number (if I remember correctly). Calculate the following.

while (n > 1) {
    if (n % 2 == 0) {
        n = n/2;
    } else {
        n = 3 ∗ n + 1;
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As you will find when you read the Wikipedia article, it has lots of names. – André Nicolas Feb 4 '13 at 7:07
up vote 7 down vote accepted

It's called the Collatz Conjecture.

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Look for "Collatz-problem" here or in wikipedia

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