A research problem which interests me is the Collatz 3x+1 function, which is defined as follows:
\begin{equation*} f(n)= \begin{cases} 3n+1 & \text{if $n$ odd ,} \\ \frac{n}{2} &\text{if $n$ even.} \end{cases} \end{equation*}
Collatz conjectured that recursively applying this function to a number always ends in the loop {1,4,2,1}.
Take for example 9.
f(9) = 28 , f(28)=14 , f(14)=7, f(7)=22 , f(22)=11 ,f(11)=34 , f(34)=17 , f(17)=52, f(52)=26, f(13)=40 ,f(40)=20, f(20)=10 , f(10)=5 , f(5)=16, f(16)=8, f(8)=4 , f(4)=2, f(2)=1, f(1)=4
et voila...
Try 27, if you dare.
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