Collatz Conjecture

Take a number number $ n $ (non-zero positive integer), if $ n $ is even, divide it by $ 2 $, else multiply by $ 3 $ and add $ 1 $. Start over with the result until you get the number $ 1 $.

Mathematically the algorithm is defined by the function $ f $: $$ f_{3n+1}(n) = \begin{cases}{ \frac{n}{2}} & {\text{if }}n \equiv 0 \mod{2} \\ 3n+1 & {\text{if }} n \equiv 1 \mod{2} \end{cases} $$

Example: $ n=10 $, $ 10 $ is even, divide it by $ 2 $ and get $ 5 $,
$ 5 $ is odd, multiply it by $ 3 $ and add $ 1 $ to get $ 16 $,
Continue the sequence to get $ 8 $, $ 4 $, $ 2 $ and $ 1 $.

The sequence is generally considered to be finished at 1, because otherwise the following numbers are 4, 2, 1, 4, 2, 1, 4, 2, 1 which are repeated endlessly.

The Collatz conjecture stipulates that the 3n+1 algorithm will always reach the number 1.

Some numbers have surprising trajectories like 27, 255, 447, 639 or 703.

No, nobody has found a number for which it does not work but nobody has found any mathematical proof that the conjecture is always true.

This is why the conjecture is also called the Syracuse problem or the Collatz problem and it is not a theorem.

Anyone finding a number that does not end at 1 will then have solved the conjecture by proving it to be false.

No, there have been some real advances recently but the Syracuse conjecture remains unsolved despite dozens of pseudo-scientists who have claimed to have a proof.

A number never appears twice in the sequence.

Any sequence ends with a series of powers of 2.

An odd number is always followed by an even number.

The numbers 5 and 32 give the same result.

// Javascript Algorithm
function step(n) {
if (n%2 == 0) return n/2;
return 3*n+1;
}
function collatz(n) {
var nb = 1;
while (n != 1) {
n = step(n);
nb++;
}
return nb;
}
// Python Code Algo
def collatz(x):
while x != 1:
if x % 2 > 0:
x =((3 * x) + 1)
list_.append(x)
else:
x = (x / 2)
list_.append(x)
return list_


The Collatz conjecture/problem is also known as

- 3n + 1 conjecture

- Hailstone conjecture

- Ulam conjecture

- Kakutani's problem

- Thwaites conjecture

- Hasse's algorithm

- Syracuse problem

- HOTPO (Half Or Triple Plus One)

This table is for numbers until 1000 (total time => numbers)

This table shows numbers until 1000 (max number reached => numbers)

Formulated in 1937 by Lothar Collatz (german mathematician), it remains unsolved: nobody has been able to prove this conjecture always ends with 1.