% Dans le préambule
% -----------------
\usepackage{pythontex}
\usepackage{tikz}
% -----------------

\begin{tikzpicture}[x=0.5mm,y=0.005mm]
\draw (0,0)--(120,0);
\draw (0,0)--(0,9300);

\begin{pycode}
i,n = 0,27
while n!=1:
    i=i+1
    if n%2==0:
        n=n//2
    else:
        n=3*n+1
    print(r"\draw(%s,%s) node{$\bullet$};"%(i,n))
\end{pycode}

\end{tikzpicture}